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WebExtensions are designed to be compatible with Chrome and Opera extensions: as far as possible, extensions written for those browsers should run on Firefox with minimal changes.

However, Firefox currently has support for only a limited set of the features and APIs supported by Chrome and Opera. We're working on adding more support, but many features are not yet supported, and we may never support some.

This article lists all features and APIs that are fully or partially supported in Firefox Developer Edition (currently Firefox 47). Where a feature is partially supported, we've indicated what the gaps are.

You should assume that features and APIs not listed here at all are not yet supported.

manifest.json features

Fully supported keys

Partially supported keys

background

Firefox does not support the "persistent" property. Background scripts stay loaded all the time.

commands

Firefox does not support:

  • Media keys as shortcuts
  • global
  • the special command _execute_browser_action

content_scripts

Firefox does not support:

  • match_about_blank

content_security_policy

Firefox does not support:

  • "http://127.0.0.1" or "http://localhost" as script sources: they must be served over HTTPS.

options_ui

Firefox does not support:

  • chrome_style

Using options_ui requires a valid value for the applications.gecko.id property.

permissions

Firefox does not support the following permissions:

  • background
  • clipboardRead
  • clipboardWrite
  • geolocation
  • unlimitedStorage

Obviously, it doesn't support permissions for APIs that are themselves not supported.

incognito

Firefox does not support the following incognito (private browsing) modes:

  • split

JavaScript APIs

Fully supported APIs

Partially supported APIs

bookmarks

  • Firefox does not support:
    • import()
    • export()
    • onCreated
    • onRemoved
    • onChanged
    • onMoved
    • onChildrenReordered
    • onImportBegan
    • onImportEnded
    • BookmarkTreeNodeUnmodifiable
  • Firefox has special bookmarks like "Recently Bookmarked" or "Recently Visited"

contextMenus

  • Firefox does not support:
    • the "browser_action" or "page_action" context types

downloads

  • Firefox does not support:
    • drag()
    • acceptDanger()
    • setShelfEnabled()
    • onDeterminingFilename
  • The saveAs option and values other than "GET" for the method option are not supported by download()

extension

  • Firefox does not support:
    • setUpdateUrlData()
  • Additionally, the following deprecated properties will not be supported:
    • onRequest
    • onRequestExternal
    • getExtensionTabs()
    • sendRequest()

idle

  • Firefox does not support:
    • onStateChanged
    • setDetectionInterval()

Additoinally, queryState() always returns "active" in Firefox, regardless of the current system idle state.

management

  • Firefox does not support:
    • LaunchType
    • get()
    • getAll()
    • getPermissionWarningsById()
    • getPermissionWarningsByManifest()
    • setEnabled()
    • uninstall()
    • launchApp()
    • createAppShortcut()
    • setLaunchType()
    • generateAppForLink()
    • onInstalled
    • onUninstalled
    • onEnabled
    • onDisabled

notifications

  • Firefox does not support:
    • update()
  • Firefox doesn't provide byUser data.

runtime

  • Firefox does not support:
    • getPackageDirectoryEntry()
    • reload()
    • requestUpdateCheck()
    • restart()
    • sendNativeMessage()
    • onBrowserUpdateAvailable
    • onConnectExternal
    • onInstalled
    • onMessageExternal
    • onRestartRequired
    • onStartup
    • onSuspend
    • onSuspendCanceled
    • onUpdateAvailable

storage

  • Firefox does not support:
    • managed storage area
    • sync storage area
    • getBytesInUse().

tabs

  • Firefox treats highlighted and active as the same, since Firefox has no concept of selecting multiple tabs.
  • In Firefox, you need the tabs permission if you want to include url in the queryInfo parameter to tabs.query().
  • In Firefox, relative URLs passed into tabs.executeScript() or tabs.insertCSS() are resolved relative to the current page URL. In Chrome, these URLs are resolved relative to the add-on's base URL. To work cross-browser, you can specify the path as an absolute URL, starting at the add-on's root, like this:

    /path/to/script.js
  • In Firefox, you can't open (using tabs.create), or navigate to (using tabs.update) privileged URLs:
    • chrome: URLs
    • javascript: URLs
    • data: URLs
    • privileged about: URLs (for example, about:config, about:addons, about:debugging)
  • Additionally, the following deprecated properties will not be supported:
    • sendRequest()
    • getSelected()
    • onActiveChanged
    • onHighlightChanged
    • onSelectionChanged

webNavigation

  • Firefox does not support:
    • onCreatedNavigationTarget
    • onTabReplaced

webRequest

  • Firefox does not support:
    • onAuthRequired
    • filtering by windowId and tabId
    • the "requestBody" instruction in opt_extraInfoSpec
  • In Firefox requests can be redirected only if their original URL uses the http or https scheme

windows

  • Firefox does not support:
    • the focused option in create()
  • In Firefox onFocusChanged will trigger multiple times for a given focus change.

Planned APIs

We don't support the following APIs, but plan to, soon:

This doesn't mean that these are the only additional APIs we will support, but that they are our current priorities.

Miscellaneous incompatibilities

Optional arguments

URLs in CSS

Firefox resolves URLs in injected CSS files relative to the CSS file itself, rather than to the page it's injected into.

Additional incompatibilities

Firefox does not support using alert() from background pages. Using alert(message) from a background page will cause the Browser Console to be opened and both a line stating "alert() is not supported in background windows; please use console.log instead." and the message will be output to the console.

Document Tags and Contributors

 Last updated by: evilpie,