Comment 39 for bug 91849

From wiki.archlinux.org:

AIGLX -- Enables GL-accelerated effects on a standard desktop.

Composite -- A Xorg extension required by composite managers
The Composite extension for X causes an entire sub-tree of the window hierarchy to be rendered to an off-screen buffer. Applications can then take the contents of that buffer and do whatever they like. The off-screen buffer can be automatically merged into the parent window or merged by external programs, called compositing managers.