Extentions

Firefox users can add features and change functionality in Firefox by installing extensions. Extension functionality is varied; such as those enabling mouse gestures, those that block advertisements, and those that enhance tabbed browsing.

Features that the Firefox developers believed would be used by a small number of its users have not been included in Firefox and left to be implemented as extensions. Many Mozilla Suite features, such as IRC chat (ChatZilla) and calendar have been recreated as Firefox extensions. Extensions are also often a testing ground for features that are eventually returned to the main codebase.[citation needed] For example, MultiZilla was an extension that provided tabbed browsing when Mozilla lacked that feature.

While extensions provide a high level of customizability, PC World notes the difficulty a casual user would have in finding and installing extensions as compared to their features being available by default.

Most extensions are not created or supported by Mozilla. As extensions have the same rights to the user's system as Firefox itself, it's possible to create malicious extensions. Mozilla provides a repository of extensions that have been reviewed by volunteers to not contain malware. Since extensions are mostly created by third parties, they do not necessarily go through the same level of testing as official Mozilla products, and they may have bugs or vulnerabilities.

Extensions, also known as add-ons, are thus installable enhancements to the Mozilla Foundation's projects (and compatible variants such as Portable Firefox), and add features to the application or allow existing features to be modified. Mozilla developers intend Firefox to be a fairly minimal browser 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. They are installed via XPInstall modules.

Extension technologies

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Primary function of extensions

Firefox extensions are generally used to add functions to the browser. Examples of functions which an extension might add include RSS readers, bookmark organizers, toolbars (for example, the Wikipedia editor toolbar), website-specific client programs, FTP, e-mail, mouse gestures, proxy server switching, or debugging 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, not on the webpage itself, but as it is displayed in an individual user's browser. For example, Adblock extensions can prevent the browser from loading images which are advertisements. Another popular extension, CustomizeGoogle, modifies how Google pages are displayed, for example by providing links to competing search engines.
Also, the Greasemonkey extension allows the user to install scripts which modify the look of specific pages or the Web in general. If a user doesn't find the script he is looking for, he can use the Platypus extension to generate his own script, which might delete content from, move content around within, or add content to a page.

Other uses

Firefox 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 parody the changes from Phoenix to Firebird to Firefox in 2003-2004.

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Updating extensions

Firefox periodically checks for updates to installed extensions, although they can be manually checked in the extension window. If the extension's install.rdf manifest contains a custom update.rdf RDF file, this will be used to check for updates. Otherwise, Firefox will look for updates at addons.mozilla.org.

Plugins

Mozilla Firefox and related software uses Add-on as an inclusive term for a category of augmentation modules that are subdivided into plugins, extensions, themes, and search engines.

Plugins are similar to extensions; both modify or add features. The common plugins are Acrobat Reader, Flash Player, Java, Quicktime, RealPlayer, Shockwave, Windows Media Player; there are about one thousand extensions.

Firefox includes a tool for managing extensions, allowing them to be listed, selectively enabled/disabled, or uninstalled. But once a plugin is installed, there is no built-in management interface for disabling or uninstalling, other than the content management tool for enabling/disabling Java (and JavaScript).

http://developer.mozilla.org provides you with all the newest and pertinent info you need concerning Firefox's development in terms of Topics (extentions, plugins, features etc...), Technologies, Mozilla Developer Center, Application and component framework, and you can also access Mozilla Developer Center blogs and MDC Webwatch for more information.

Source: http://www.wikipedia.com

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