glXWaitVideoSync sometimes gets throttled on XWayland
See the following Mozilla bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1592786
Firefox needs vsync events to trigger its rendering pipeline. This is currently done on GLX by spawning a separate thread which has a loop with glXWaitVideoSync. This works perfectly on plain X11, however on XWayland it will randomly start falling back to 30fps on a 60fps monitor (missing every other event).
I thought the issue might be the renderer thread blocking on swapbuffers and holding a lock, however as far as I can tell there aren't any such locks.