There are 2 repositories under xulrunner topic.
Komodo Edit is a fast and free multi-language code editor. Written in JS, Python, C++ and based on the Mozilla platform.
DEPRECATED: Multiplatform GUI Prototyping/Wireframing
live XUL editor : with seamonkey open this --->
a frontend for Fudan eLearning, with many new feature added.
UXP - Unified XUL Platform
AdBlock for GeckoFX WebBrowser. Custom keyword/domain support + EasyList, EasyPrivacy & AdGuard blocklists
Catalog of classic Firefox add-ons created before WebExtensions apocalypse