This is a metabug to track the bugs blocking the switch to use threaded compositor in the GTK+ port.
We have switched to threaded compositor already. There are a few bugs blocking this one yet, but we asked if those problems are still present with no reply. The other bug blocking this is the meta bug for layout tests that started to fail after the switch, but they are not blockers. Se, I'm closing this now.
We already switched and this bug is closed, so this can't depend on anything else. Also, the problem in bug #165246 seems to be the accelerated compositing mode, not the threaded compositor.