WHAT IS addons?
Add-ons are small pieces of software that add new features or functionality to your installation of Firefox Add-ons allow users to add or increase the application features, use the theme to their liking, and handle new types of material.
The 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 very popular with Firefox, because Mozilla developers intend to develop applications that the browser be minimalist enough to reduce the bugs, while retaining flexibility, so that individual users can add the features they want.
Common plugins include Acrobat Reader, Flash Player, Java, Quicktime, RealPlayer, Shockwave, and Windows Media Player.
Additional skins that can be mounted to the add-on you.
Unlike the Persona which only provide a background picture to your browser's Menu Bar, the theme is usually also change the Buttons on your browser.