Yet another userChrome.js manager

The files in this repository create a toolkit to load arbitrary javascript files to be run in Firefox browser context. This method relies on autoconfig functionality available in Firefox.

Overview

Files in program folder tell Firefox to load an additional javascript module file from the current Profile directory. The boot.sys.mjs is the one that implements loading and managing additional files.

Since the files in program go to the main program installation path, they will affect all profiles that are being run using that executable.

However, the bulk of the logic is located in profile folder with boot.sys.mjs so if the file is not found there then the loader is simply not used.

The loader module (boot.sys.mjs) depends on two additional files: utils.sys.mjs to which is collection of various helper functions you can use in your scripts and fs.sys.mjs to implement read and write operations on the file system.

Note as of version "0.8" fx-autoconfig is incompatible with Firefox ESR 102

Warning!

Please note that malicious external programs can now inject custom logic to Firefox even without elevated privileges just by modifying boot.sys.mjs or adding their own script files.

Install

Setting up config.js from "program" folder

Copy the contents of the directory called "program" (not the directory itself) into the directory of the Firefox binary you want it to apply to.

This means that if you want to affect multiple installations, like release, beta, ESR etc. you need to add the files to all of them.

Setting up profile

Copy the contents of the folder "profile" (not the folder itself) to the Firefox profile folder that you want to modify. If the profile already has a chrome folder (for userChrome.css or userContent.css) then the chrome folders should merge. Otherwise the chrome folder will be created. You should end up with chrome folder in the profile root, and three folders inside it - JS, resources and utils.

There will be three files in the chrome/utils/ folder:

• chrome.manifest - registers file paths to chrome:// protocol
• boot.sys.mjs - implements user-script loading logic
• fs.jsm - implements filesystem-related functions - boot.sys.mjs uses this file internally.
• utils.sys.mjs - implements various functions used by utils.sys.mjs and which your scripts can also use

Deleting startup-cache

Firefox caches some files to speed-up startup. But the files in utils/ modify the startup behavior so you might be required to clear the startup-cache.

If you modify boot.sys.mjs and happen to break it, you will likely need to clear startup-cache again.

Usage

The loader module boot.sys.mjs looks for three kinds of files in your scripts directory ("JS" by default - can be changed in chrome.manifest):

• <filename>.uc.js - classic script which will be synchronously injected into target documents.
• <filename>.uc.mjs (new in 0.8) - script which will be loaded into target documents asynchronously as ES6 module.
• <filename>.sys.mjs - module script which will be loaded into global context synchronously once on startup

Additionally (".uc.js") scripts can be marked as background-module by tagging them with @backgroundmodule in the script header.

Just put any such files into the JS directory. The JS directory should be in the same directory where userChrome.css would be. If you wish to change the directory name then you need to modify the chrome.manifest file inside utils directory. For example change ../JS/ to ../scripts/ to make Firefox load scripts from "scripts" folder.

At runtime, individual scripts can be toggled on/off from menubar -> tools -> userScripts. Note that toggling requires Firefox to be restarted, for which a "restart now" -button is provided. The button clears startup-cache so you don't need to worry about that.

For window scoped scripts (classic .uc.js and .uc.mjs) it the toggling should take effect when a new window is opened. Any effects in the old window will persist though.

A global preference to toggle all scripts is userChromeJS.enabled. This will disable all scripts but leaves the restart-button in the custom menu available.

Styles

From version 0.8.5 onwards the loader also supports injection of styles. The default directory where loader looks for them is chrome/CSS/ which again can be re-mapped by modifying chrome/utils/chrome.manifest

File name of styles must end with .uc.css which the loader will pick up automatically - just like scripts. By default, scripts are injected in author mode only into browser.xhtml - you can register other targets using the header @include directives just like scripts.

Alternatively you can use @stylemode agent_sheet directive in header to make loader register it as agent style. User styles are not supported currently - just use userChrome.css for that.

Notice that the header format for styles is slightly different than it is for scripts because CSS doesn't support // line comments.

Filenames

Script files (among other things) are loaded using chrome:// protocol. Chrome urls are of form:

chrome://<package>/<provider>/<path>

eg.

chrome://userscripts/content/my_script.uc.js

Notable for the path part, it must start with [a-zA-Z0-9] and as such the loader module only tries to seek script files where the filename starts with alphanumeric character. Note that files in sub-directories can still start with some other character.

Same limitation also applies to all other uses of chrome:// urls, such as if you try to load some file from your resources directory using chrome url.

See more about chrome url canonification at searchfox

API

This manager is NOT entirely compatible with all existing userScripts - specifically scripts that expect a global _uc object or something similar to be available. This manager does export a _ucUtils object to window objects which is described in Utils section.

Script scope

Each script normally runs once per document when the document is loaded. A window is a document, but a window may contain several "sub-documents" - kind of like iframes on web pages, an example of this is the sidebar.

@include & @exclude

By default, the loader executes your script only in the main browser window document. Using any @include header will override the default - for example:

// ==UserScript==
// @include           chrome://browser/content/places/places.xhtml
// ==/UserScript==

The above would be executed only in the Library window.

// ==UserScript==
// @include           main
// @include           chrome://browser/content/places/places.xhtml
// ==/UserScript==

This would execute in both library and main window. main is an alias for chrome://browser/content/browser.xhtml in Firefox and chrome://messenger/content/messenger.xhtml in Thunderbird

A wildcard * can be used to target any window.

// ==UserScript==
// @include           *
// @exclude           main
// ==/UserScript==

This would execute in all documents, excecpt main window - notice "main" is excluded this time.

In addition, scripts can be marked as @backgroundmodule in which case they are executed "outside" of any document when the the loader reads the file. See backgroundmodule section below.

Some convenience functions are provided for scripts to use in global _ucUtils object available in windows.

@backgroundmodule

Scripts can be marked as background modules by including a @backgroundmodule line in script header. See example:

// ==UserScript==
// @name           example background module
// @note           Loading as background module
// @backgroundmodule
// ==/UserScript==

let EXPORTED_SYMBOLS = [];
...
// actual script here

Alternatively, you can name your script with .sys.mjs file extension in which case the loader automatically treats it as backgroundmodule.

Note that the EXPORTED_SYMBOLS array like above in module global scope is mandatory in .uc.js scripts when they are loaded as backgroundmodule. It is not necessary in .sys.mjs scripts.

ES6 modules

// ==UserScript==
// @name           example sys.mjs module
// ==/UserScript==

import { Some } from "chrome://userscripts/content/modules/some.sys.mjs";
// This would import the script from "modules" sub-directory of your scripts folder.
// Note that such script would not be loaded by boot.jsm itself.

Some.doThing();
...

The manager loads any .sys.mjs files always as backgroundmodule - in addition they are loaded as ES6 modules which means you can use static import and export declarations inside them.

You should note that background modules do not have access to window objects when they are being run because they are executed before any window exists. Thus, they also do not automaticalle get access to _ucUtils object.

As of version 0.8 ES6 module scripts, including backgroundmodules (so .sys.mjs and .uc.mjs files) can import _ucUtils like this:

import { _ucUtils } from "chrome://userchromejs/content/utils.sys.mjs";

Although window scoped module scripts (.uc.mjs) automatically gain access to it anyway from the window object.

import heads-up

Note for .uc.mjs scripts! Because your script is running in its own module scope within a window the module imported with an import statement above is NOT the same instance of the object as what you would get automatically via _ucUtils. The methods within are the same, but since it is a different object its internal properties have not been initialized by boot.sys.mjs so some functionality is missing - such as access to custom script info via .getScriptData()

You can instead use ChromeUtils to import the same object from the global object:

const { _ucUtils } = ChromeUtils.importESModule("chrome://userchromejs/content/utils.sys.mjs")

Or indeed just use _ucUtils from the window object.

The same behavior applies to all modules imported from .uc.mjs module scopes via import statements.

@description

The @description header can be used to store short description in script meta-data.

// ==UserScript==
// @description    simple test script that does nothing
// ==/UserScript==

@long-description

Normally @description stores the text appearing on the same line as the header itself. However, when @long-description is present the description will be a block comment starting from the next line after the @description header:

// ==UserScript==
// @long-description
// @description    this-part-is-now-ignored
/*
Here goes my long description about this mighty powerful script.
It does all the things and even more!
...
or at least that's the plan, it actually does nothing currently :p
*/
// ==/UserScript==

Note that the single-line part of @description is now ignored. But you can put something there as fallback value for loaders that don't have multi-line description support.

@ignorecache

This header can be used to mark scripts that should not be put into startup-cache. Instead, such scripts are always read from disk when loaded.

// ==UserScript==
// @name           example ignorecache file
// @ignorecache
// ==/UserScript==

console.log("Hello world!")

This script would log "Hello world!" to console when new window is opened. Normally if you would change this script content and then open a new window, then Firefox would still log "Hello world!" because the script is cached.

However, by ignoring cache the file is loaded from disk every time its used, thus changes will be reflected immediately (but not for the window the script has already been loaded into).

This header may be useful while developing a script, but you should leave caching enabled most of the time.

Note: if your script has already been cached once, then you need to clear startup-cache once to make it ignore cache. In other words, you can't add this header to existing script to make it ignore cache immediately.

@loadOrder

// ==UserScript==
// @name           example
// @loadOrder      3
// ==/UserScript==

console.log("This script is loaded sooner than default")

Load-order is treated as positive integer (including 0) By default scripts have load-order 10. Scripts with load-order <10 are injected before unmarked scripts and >10 are loaded after them.

If load-order is not specified then scripts follow normal filename alphabetical ordering.

Note: All Scripts marked as backgroundmodule will have load-order -1

@onlyonce

By default the script is executed once per document it applies to, but this can be changed with @onlyonce header in which case the script will only be run in the first document.

// ==UserScript==
// @name           example only-once file
// @onlyonce
// ==/UserScript==

console.log("Hello world!") // This is only run in the first window that opens.

@startup

Scripts can define a function to be executed when they are loaded in the header portion of the script. Consider the following header:

// ==UserScript==
// @name            My Test Script
// @onlyonce
// @startup         myScriptObject

This tells the loader to execute this script file only once per session because of @onlyonce directive. But the header also tells the loader to execute a special function named _startup from sharedGlobal.myScriptObject on each window. This makes it possible to do some global initialization work once and then run only the _startup function for each window created afterwards.

The _startup function will receive one argument - reference to the window object where it was executed.

In short, to use startup directive you need to store an object named myScriptObject to the sharedGlobal object and the myScriptObject must have a property called _startup.

_ucUtils.sharedGlobal.myScriptObject = {
  _startup: function(win){ console.log(win.location) }
}

NOTE This is behavior is completely incompatible with the way old userscripts implement startup - which generally was of form eval(<whatever_is_in_header_startup>)

@stylemode (styles only)

Default value is author_sheet - valid values are author_sheet and agent_sheet

/* ==UserScript==
// @name           agent style sheet
// @description    an example for @stylemode directive
// @stylemode      agent_sheet
// ==/UserScript== */

Tells the loader in which mode this style should be injected. Agent sheets are global, author sheets are per document you inject them into (default browser.xhtml)

@usefileuri (styles only)

Tells the loader to register this style using its file:/// url instead of chrome:// url.

/* ==UserScript== // @name author style sheet // @usefileuri // ==/UserScript== */

Note that some CSS features may not be available for file:// uri styles. However, chrome:// styles cannot be modified using devtools, while file:// uri styles can be.

Utils

General

_ucUtils.createElement(document,tagname,attributes,isHTML) -> Element

_ucUtils.createElement(document,"menuitem",{ id:"someid", class:"aClass", label:"some label" })

Attaches a new element with tagname to the given document and adds it attributes from attributes object. isHTML is a boolean indicating whether the element is XUL element or HTML element - defaults to false.

_ucUtils.createWidget(details) -> <Widget wrapper object>

_ucUtils.createWidget({
  id: "funk-item",                // required
  type: "toolbaritem",            // ["toolbaritem","toolbarbutton"]  
  label: "funky2",                // opt (uses id when missing)
  tooltip: "noiseButton",         // opt (uses id when missing)
  class: "noiseButton",           // opt additional className (see below for more)
  image: "favicon.png",           // opt image filename from resources folder
  style: "width:30px;",           // opt additional css-text (see below for more)
  allEvents: true,                // opt trigger on all clicks (default false)
  callback: function(ev,win){     // Function to be called when the item is clicked
    console.log(ev.target.id)
  }
})

Widget is a wrapper for actual elements. Firefox tracks widget placements across windows meaning that you can create the widget once and then you can re-position it using customize mode and its new location will be shared in all windows. The wrapper contains information about the instances of that widget in windows.

The class of elements using this will by default be "toolbarbutton-1 chromeclass-toolbar-additional" and the value of the class property (when provided) will be added into that.

The style info will be added as inline style to all elements of that widget. The image will be loaded as centered background-image in toolbaritems and as list-style-image in toolbarbuttons.

The callback function will be stored in _ucUtils.sharedGlobal mapped to the provided id. Clicking the button will call the callback which will receive two arguments: event (click) and window which is a reference to the window object where that instance of the widget is.

If the callback property is not a function, then the widget will be just a passive element.

The allEvents property defines if the callback should be called for all clicks, not just left-clicks.

The image is loaded from resources folder so save your icon files there.

This method will throw if:

• id is not provided
• type is anything except "toolbaritem" or "toolbarbutton"
• A widget with same id already exists. For example if a script which calls this method is executed in multiple Firefox windows then the first one should succeed, but successive calls should throw an Error.

_ucUtils.registerHotkey(details,function) -> Boolean

// description for hotkey Ctrl + Shift + G
let details = {
  id: "myHotkey",
  modifiers: "ctrl shift",
  key: "G"
}

function onHotkey(window,hotkey){
  console.log(hotkey);
  // prints id, modifiers and key of the pressed hotkey.
  // window is the window-object that captured this hotkey
}

let success = _ucUtils.registerHotkey(details,onHotkey);

Register a hotkey handler to each browser window. registerHotkey returns true if the hotkey was registered correctly. false if there was a problem. id,modifiers and key fields are mandatory and must be String type.

The function only supports modifiers "alt", "shift", "ctrl", "meta" and "accel" modifiers. Valid key values are A-Z a-z - and function keys F1-F12.

The created hotkey will override built-in hotkeys.

The id field in the details object should have some unique value, but this is not enforced.

_ucUtils.getScriptData(aFilter) -> Array | ScriptInfo

Returns ScriptInfo object(s) with a copy of their metadata. This includes scripts that are not yet running or which are disabled by pref.

When called without arguments returns an array of ScriptInfo objects describing your scripts.

let scripts = _ucUtils.getScriptData(); 
for(let script of scripts){
  console.log(`${script.filename} - @{script.isEnabled} - ${script.isRunning}`)
}

If the first argument is a string then this returns a single ScriptInfo object for a script that had the specified filename. If such script is not found then null is returned.

let script = _ucUtils.getScriptData("my-script.uc.js");
console.log(`@{script.name} - ${script.isRunning}`);

If the first argument is a function, then this function returns a filtered list of scripts that return true when the function is run on them:

let scripts = _ucUtils.getScriptData(s => s.isRunning);
console.log(`You have ${scripts.length} running scripts);
// This is essentially the same as _ucUtils.getScriptData().filter(s => s.isRunning)

Note! If the first argument is anything other than a function or a string, then getScriptData() will throw an error.

_ucUtils.parseStringAsScriptInfo(aName, aString) -> ScriptInfo

This can be used to construct a ScriptInfo object from arbitrary string following the same logic the loader uses internally. When given aName as "filename" the aString is parsed just like script metadata block in your files.

let myMetadataBlock = `// ==UserScript==
// @name           my-test-info
// @description    Constructed ScriptInfo
// ==/UserScript==
`;

let scriptInfo = _ucUtils.parseStringAsScriptInfo("fakeFileName",myMetadataBlock);
console.log(scriptInfo.name)
// "my-test-info"

Note! There needs to be a new-line after the closing // ==/UserScript== "tag" for the metadata to be parsed correctly.

_ucUtils.windows -> Object

Returns an object to interact with windows with two properties

_ucUtils.windows.get(onlyBrowsers) -> Array

Return a list of handles for each window object for this firefox instance. If onlyBrowsers is true then this only includes browser windows. If it's false then it also includes consoles, PiP, non-native notifications etc.

onlyBrowsers defaults to true.

_ucUtils.windows.forEach(function,onlyBrowsers)

_ucUtils.windows.forEach((document,window) => console.log(document.location), false)

Runs the specified function for each window. The function will be given two arguments - reference to the document of the window and reference to the window object itself.

Note! _ucUtils may not be available on all target window objects if onlyBrowsers is false. The callback function should check for it's availability when called that way.

_ucUtils.toggleScript(fileName or element) -> Object or null

filename:

_ucUtils.toggleScript("test.uc.js")

Element where this is a menuitem:

_ucUtils.toggleScript(this);

If the argument is an element the function reads a filename attribute from the element and uses that. Toggles the specified script, note that browser restart is required for changes to take effect.

The return value is null if a matching script was not found. Otherwise, the return value is an object { script: filename, enabled: true|false }

_ucUtils.loadURI(window,details) -> boolean

_ucUtils.loadURI(window,{
  url:"about:config",
  where:"tab",        // one of ["current","tab","tabshifted","window"]
  private: true,      // should the window be private
  userContextId: 2    // numeric identifier for container
});

// "tabshifted" means background tab but it does not work for unknown reasons
// Private tabs cannot be created in non-private windows

Return a boolean indicating if the operation was successful. "url" and "where" properties are mandatory - others are optional.

_ucUtils.restart(clearCache)

Immediately restart the browser. If the boolean clearCache is true then Firefox will invalidate startupCache which allows changes to the enabled scripts to take effect.

_ucUtils.startupFinished() -> Promise

_ucUtils.startupFinished()
.then(()=>{
  console.log("startup done");
});

Returns a promise that will be resolved when all windows have been restored during session startup. If all windows have already been restored at the time of calling the promise will be resolved immediately.

_ucUtils.windowIsReady() -> Promise

_ucUtils.windowIsReady(window)
.then(()=>{
  console.log("this window has finished starting up");
});

This corresponds to browser-delayed-startup-finished event. Note that extension-engine initialization code may or may not have run when this promise resolves.

Difference of startupFinished and windowIsReady

Since scripts run per window, startupFinished will be resolved once in each window that called it when ALL those windows have been restored. But windowIsReady will be resolved whenever the particular window that calls it has started up.

_ucUtils.showNotification(details) -> Promise

_ucUtils.showNotification(
  {
    label : "Message content",  // text shown in the notification
    type : "something",         // opt identifier for this notification
    priority: "info",           // opt one of ["system","critical","warning","info"]
    window: window.top ,        // opt reference to a chromeWindow
    tab: gBrowser.selectedTab,  // opt reference to a tab
    buttons: [...],             // opt array of button descriptors
    callback: () => {}          // opt function to be called when notification is dismissed
  }
)

Priority defines the ordering and coloring of this notification. Notifications of higher priority are shown before those of lower priority. Priority defaults to "info".

If window key exists then the notification will be shown in that window. Otherwise it is shown in the last active window.

If tab key exists then the notification will be shown in that tab only. Otherwise the notification is global to the window.

See more about buttons and callback keys at notificationbox.js

_ucUtils.updateStyleSheet(name, sheet_mode) -> boolean

_ucUtils.updateStyleSheet() // reloads userChrome.css

 // reloads a style in author-mode stylesheets list with matching name
_ucUtils.updateStyleSheet("userChrome.au.css","author")

 // reloads a style in agent-mode stylesheets list with matching name
_ucUtils.updateStyleSheet("userChrome.ag.css","agent")

Argument filename is relative to resources folder, but you can use ../ prefix to get back to chrome folder.

Note, you can't reload a style that is in one sheet-mode list into another sheet-mode. Such as, you cannot use this to reload userChrome.css into agent-mode list.

Return value true/false indicates wheter a style file with specified name was found in the corresponding list.

If the specified stylesheet imports other files, then calling this will also reload any of those imported files. However, in experience it might be that reload of imported stylesheets does not take effect until a new window is created.

Prefs

A shortcut for reading and writing preferences

_ucUtils.prefs.set(prefName,value) -> undefined

_ucUtils.prefs.set("some.pref.path","test");
_ucUtils.prefs.set("some.other.pref",300);

This will throw if you try to set a pref to a value of different type than what it currently is (ie. boolean vs. string) unless the pref doesn't exist when this is called. This will also throw if you try to set the pref with value that is not one of number, string, boolean - number is also converted to integer.

_ucUtils.prefs.get(prefName) -> Pref

Returns a representation of the pref wrapped into an object with properties:

let myPref = _ucUtils.prefs.get("userChrome.scripts.disabled");
/*
* {
*   exists() // true|false indicating if this pref exists
*   name     // string - the called pref name
*   value    // <number|string|boolean> | `null` - null means pref with this name could not be read
* set value() // same as _ucUtils.prefs.set(name,value)
*   hasUserValue() // true|false indicating if this has user set value
*   type     // "string"|"boolean"|"number"|"invalid"
*   reset()  // resets this pref to its default value
* }
*/

myPref.exists()
// false - "userChrome.scripts.disabled" does not exist

_ucUtils.prefs.addListener(prefName,callback) -> Object

let callback = (value,pref) => (console.log(`${pref} changed to ${value}`))
let prefListener = _ucUtils.prefs.addListener("userChromeJS",callback);

Note that the callback will be invoked when any pref that starts with userChromeJS is changed. The pref in callback argument will be a Pref object wrapping the value of the actual pref whose value was changed.

_ucUtils.prefs.removeListener(listener)

_ucUtils.prefs.removeListener(prefListener) // from above example

Pref class can also be imported directly to module scripts like this:

import { Pref } from "chrome://userchromejs/content/utils.sys.mjs";

Filesystem general

Scripts should generally use the resources folder for their files. The helper functions interacting with filesystem expect resources to be the root folder for script operations.

The resources folder is registered to chrome:// scheme so scripts and stylesheets can use the following URL to access files within it:

"chrome://userChrome/content/<filename>.txt" 

Scripts folder is registered to: chrome://userScripts/content/

The loader module folder is registered to chrome://userchromejs/content/

_ucUtils.openScriptDir() -> Boolean

_ucUtils.openScriptDir();

Tries to open your script directory in OS file manager. Returns true or false indicating success. Whether this works or not probably depends on your OS. Only tested on Windows 10.

Filesystem _ucUtils.fs

These APIs exist starting from versioned release "0.7".

Main idea is that various methods return a FileSystemResult object instead of the actual operation result directly.

The FileSystemResult result object is one of four types:

• Filesystem.RESULT_FILE get reference to a file
• Filesystem.RESULT_DIRECTORY get referece to a directory
• Filesystem.RESULT_ERROR non-existent file or other kind of error
• Filesystem.RESULT_CONTENT file read operation results

The result object has various methods to access underlying data.

// return nsIFile object representing either a file a directory
// throws if called on CONTENT or ERROR types
fsResult.entry()

// return the file text content as string
// throws if called on anything except CONTENT type
fsResult.content() // returns content that was read 

// return an iterator over files in a directory
// Note, the individual entries are nsIFile objects, not wrapped `FileSystemResult`s
// throws when called on anything except DIRECTORY type
fsResult.entries()
// entries() is called internally if you try to iterate over the result:
fsResult = _ucUtils.getEntry("my_dir");
for(let file of fsResult){
  ...
}

// size of read content or size of the file on disk
fsResult.size

// Read the content of this FileSystemResult
// throws if called on non-FILE type
let content = await fsResult.read() // Async read
console.log(content);
<< "Hello world!"

// throws if called on non-FILE type
let sync_content = fsResult.readSync();
console.log(content);
<< "Hello world!"

// get a file URI for this result
console.log(fsResult.fileURI)
<< file:///c:/temp/things/some.txt

// Tries to open a given file entry path in OS file manager.
// Returns true or false indicating success.
// Whether this works or not probably depends on your OS.
// Only tested on Windows 10.
fsResult.showInFileManager()

_ucUtils.fs.getEntry(fileName) -> FileSystemResult

let fsResult = _ucUtils.fs.getEntry("some.txt");
result.isFile()
// true

let nonexistent = _ucUtils.fs.getEntry("nonexistent.txt");
nonexistent.isError()
// true

let dir = _ucUtils.fs.getEntry("directory");
dir.isDirectory()
// true

_ucUtils.fs.readFile(fileName) -> Promise<FileSystemResult>

Asynchronously read a file. Throws if the argument is not a string

let fsResult = await _ucUtils.fs.readFile("some.txt");
fsResult.isFile()
// false
fsResult.isContent()
// true
console.log(fsResult.content())
// "Hello world!"

_ucUtils.fs.readFileSync(some) -> FileSystemResult

Synchronously read a file. The argument can be either a string representing filename or referece to a nsIFile object.

let fsResult = _ucUtils.fs.readFileSync("some.txt");
fsResult.isContent()
// true
console.log(fsResult.content())
// "Hello world!"

_ucUtils.fs.readJSON(fileName) -> Promise<Object | null>

Asynchronously try to read a file and parse it as json. If file can't be parsed then returns null.

let fsResult = await _ucUtils.fs.readJSON("some.json")

_ucUtils.fs.writeFile(fileName, content, options) -> Promise<Number>

let some_content = "Hello world!\n";
let bytes = await _ucUtils.fs.writeFile( "hello.txt", some_content );
console.log(bytes);

<< 13

Write the content into file as UTF8. On successful write the promise is resolved with number of written bytes.

By default writing files using this API is only allowed in resources directory. Calling writeFile with fileName like "../test.txt" will then reject the promise. You must set pref userChromeJS.allowUnsafeWrites to true to allow writing outside of resources.

Note! Currently this method replaces the existing file if one exists.

The optional options argument is currently only used to pass a filename for temp file. By default it is derived from fileName.

_ucUtils.fs.chromeDir() -> FileSystemResult

Returns FileSystemResult with type DIRECTORY for the profile chrome directory

let fsResult = _ucUtils.fs.chromeDir();
let uri = _ucUtils.chromeDir.fileURI // a file:/// uri

for (let file of fsResult){ // equal to fsResult.entries()
  console.log(file.leafName);
}

Shared global object

If scripts need to store information to a global object they can get reference to that as follows:

let global = _ucUtils.sharedGlobal

The information in the global object is available for all scripts

Startup Error

Did you experience broken Firefox startup with message banner:

"fx-autoconfig: Startup is broken"

Did it provide you with a button to "Enable workaround"? And after restart you got another banner message:

"fx-autoconfig: Something was broken in last startup"

Clicking the button sent you here, right? So what is going on here? Fear not! Here's what's happening... probably.

In older versions of this loader script, boot.sys.mjs had a hack to make a Firefox internal gBrowser object available for your custom scripts. However, said hack is now disabled by default in latest versions of boot.sys.mjs.

So, if boot.sys.mjs detects that startup has been broken because gBrowser is not available, it will show said banner. Clicking the "Enable workaround"-button will tell boot.sys.mjs to set a pref userChromeJS.gBrowser_hack.enabled to true on next startup. You can always set that pref manually if you wish.

Note: there's is also related pref userChromeJS.gBrowser_hack.required which boot.sys.mjs uses to tell itself that startup was broken on last run. Neiter the .required or .enabled pref might not exist if the loader has not detected broken startup.

If you later want to disable the "gBrowser hack" then you need to set both userChromeJS.gBrowser_hack.enabled and userChromeJS.gBrowser_hack.required to false - or simply removing both prefs.

What causes this error?

Somewhere in your custom scripts you are using gBrowser object which is not necessarily available at the time you are executing your script. Do note however, that you don't have to be using gBrowser directly in your script, it may happen as a side-effect of accessing some other internal object.

One notable example is if you try to access gURLBar - that will internally end up accessing gBrowser - which does not exist and that will break startup.

What can you do to not rely on gBrowser?

Think about when your script needs to run and you have some options:

• Wait until windows have been restored before running functions that access gBrowser. One method for that would be: _ucUtils.startupFinished().then(myFunctionAccessinggBrowser)

• Check in your function whether gBrowser is available, and if not use _gBrowser instead.

• Apply the original hack that was done by boot.jsm:

if(window._gBrowser){
  window.gBrowser = window._gBrowser;
}

Note that the second option does not work if gBrowser is accessed as a side-effect of using something else. For example, if you accessed gURLBar, then you might be able to (depending what you try to do) instead get reference to urlbar element and use that:

  gURLBar.someproperty // old
  document.getElementById("urlbar").someproperty // replacement

Or you can simply set userChromeJS.gBrowser_hack.enabled to true

Tests

Very WIP

There are few simplistic tests inside the test_profile directory. To run them you need to launch Firefox with command-line arguments pointing Firefox to use the test_profile folder as a non-relative profile. That would go for example like this:

firefox -profile "C:/things/fx-autoconfig/test_profile"

Test results should be printed to browser console.