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From Wikipedia, the free encyclopedia

Add-ons are installable enhancements to the Mozilla Foundation's projects (and compatible variants such as Portable Firefox). Add-ons allow the user to add or augment application features, use themes to his or her liking, and handle new types of content.


Types of Add-ons



Extensions can be used to modify the behavior of existing features to the application or add entirely new features. Extensions are especially popular with Firefox, because Mozilla developers intend for the browser to be a fairly minimalistic application in order to reduce software bloat and bugs, while retaining a high degree of extensibility, so that individual users can add the features that they prefer.

Extension technologies

  • CSS (Cascading Style Sheets)
  • DOM (Document Object Model) – Used to change XUL in real-time or to edit HTML that is currently loaded
  • JavaScript – The primary language of Mozilla browsers
  • XPCOM (Cross-Platform Component Object Model)
  • XPConnect
  • XPI (Cross-Platform Installer)
  • XUL (XML User Interface Language) – Used to define the UI (User Interface) and interaction with user.


Adding features

Extensions are generally used to add functions to the application. Examples of functions which an extension might add include RSS readers, bookmark organizers, toolbars, website-specific client programs, FTP, e-mail, mouse gestures, proxy server switching, or developer tools. Many Firefox extensions implement features formerly part of the Mozilla Suite, such as the ChatZilla IRC client and a calendar.

Modifying how the user views web pages

Many extensions can change the content of a webpage as it is rendered. For example, Adblock extensions can prevent the browser from loading images which are advertisements. Another popular extension, Greasemonkey, allows the user to install scripts which modify a targeted subset of webpages on the fly in a manner which is the programmatic complement to user style sheets.

Other uses

Extensions also exist for frivolous, humorous or satirical purposes. Some allude to historical features of the Firefox browser, for example restoring the "delicious delicacies" placeholder text removed in Firefox 0.9, or generating random browser names to allude to the Firefox name changes.


Common plugins include Acrobat Reader, Flash Player, Java, Quicktime, RealPlayer, Shockwave, and Windows Media Player.[IDM]

Compatibility and updates

Add-ons contain files with metadata utilized by the mechanism which controls add-on installation. Among other things, this file identifies maximum and minimum versions of a Mozilla project application with which the add-on may be used. If an attempt is made to install the add-on on a version outside of this range, it will install but will be disabled. Add-ons will often work outside of their compatibility range, and indeed some advanced users edit the metadata file to allow the released version of the add-on to run on their install. It is even possible to override the compatibility check using the Nightly Tester Tools extension.

The success of a formal compatibility check is no guarantee the add-on will work, however.

The add-on manager periodically checks for updates to installed add-ons, although checks for updates can be manually initiated by the user. By default, the update service will look for updates at Mozilla Add-ons, but if the developer includes provisions to check elsewhere, the service will do so.

See also

External links


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