Introduction
Extensions come an installable sweetening to the Mozilla Firefox or Mozilla web browsers, and add features to the application or even allow existent features to become modified.

Examples of enhancemnets to the basic capabilities of the web browser come adding an RSS reader, Bookmark organizer, Toolbar, website-specific client programs, FTP, mail, etc.

Extension technologies
JavaScript – The primary language of Mozilla Browsers XUL (XML User Interface Language) – Used to define a UI (User Interface) and interaction by owning user. DOM (Document Object Model) – Used to vary XUL inside real-period or even to edit HTML that is presently loaded CSS (Cascading Style Sheets) XPCOM/XPConnect

Other uses
Firefox extensions besides survive for even frivolous, humourous or satiric purposes. A bit of allude to historical features of a Firefox web browser, e.g. restoring the "delicious delicacies" placeholder text removed around Firefox 0.Ennead, or even getting random web browser list to parody a changes from either Phoenix to Firebird to Firefox inside 2003-4.