A group is a collection of several projects.
If you organize your projects under a group, it works like a folder.
You can manage your group member’s permissions and access to each project in the group.
XUL extensions for UXP
Here are XUL extensions - forked from their Firefox originals as well as brand new ones targeted towards the Unified XUL Platform that carries onward with XUL/XPCOM technologies abandoned by Mozilla in 2017 for being 'obsolete'.