Learn the basics of developing an extension on the Mozilla platform with this section full of beginner's guides.
Once you know the basics, these guides will help you with intermediate to advanced extension development topics.
Add-ons aren't just for Firefox. Learn how to extend other Mozilla applications, such as the Thunderbird mail client and Firefox for mobile devices.
Style Mozilla applications the way you want with pixel-perfect themes.
Find information on Search Plug-ins, Jetpack, Themes, and other types of add-ons here.