Firefox add-ons

XPInstall (Cross-Platform Install) was a technology used by the Mozilla Application Suite, SeaMonkey, Mozilla Firefox, Mozilla Thunderbird and other XUL-based applications for installing Mozilla extensions that add functionality to the main application. Support for XPInstall was removed from Firefox in November 2017 with the release of Firefox 57.

Mozilla term for software modules that can be added to the Firefox web browser and related applications

legacy compressed Zip file format