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In this article are some ways you can customize Firefox to better suit your needs.
Rearrange, hide, add, and remove toolbars and toolbar items (icons, buttons, text boxes, etc.) in Firefox. For more information, Customize Firefox controls, buttons and toolbars
Add-ons are small pieces of software which change or add to the appearance or functionality of Firefox. There are three kinds of add-ons: extensions, themes, and plugins.
Extensions: Extensions add new functionality to Firefox. They can add anything from a toolbar button to a completely new feature. They allow the application to be customized to fit the personal needs of each user while minimizing the size and appearance of the application itself. Themes: Themes modify the appearance of Firefox and allow you to personalize it to your taste. A theme can simply change the appearance of toolbar buttons, or it can completely change the look and feel of Firefox. Plugins: Plugins help Firefox perform specific functions like viewing special graphic formats or playing multimedia files. Plugins are slightly different from extensions, which modify or add to existing functionality. A typical purpose of a plugin is to add multimedia capabilities, such as the ability to embed and play videos on a web page.
For more information, see Find and install add-ons to add features to Firefox.