Are you on linux? For a while I've been running into issues with FF where it will randomly halt repainting after switching tabs. The process is clearly still responding to keystrokes and mouse events, but the ui is mostly frozen.
I've also been running into an annoying issue where hover menus will randomly stop working---it seems like the mouseout event is firing before the click event is handled.
I've also been running into an annoying issue where hover menus will randomly stop working---it seems like the mouseout event is firing before the click event is handled.
But all in all not annoying enough to switch.