User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:31.0) Gecko/20100101 Firefox/31.0 (Beta/Release) Build ID: 20140716183446 Steps to reproduce: I opened <http://www.kongregate.com/games/ConArtists/the-last-stand-dead-zone> and selected the Flash applet's full-screen option. I got a beachball cursor and Firefox failed to respond for 15-30 seconds while Flash decided to crash. (I realize that the Flash crash itself is not Firefox's fault.) Once Firefox itself became responsive again and showed the crashed-plugin placeholder, the MacOS menubar failed to reappear. Instead, I can just see desktop background there. If I focus another application, the menubar reappears, and if I focus Firefox again, the menubar disappears. If I click in the menubar area while Firefox is focused, Finder becomes the focused application (and the menubar reappears). I have found no way to recover the menubar while Firefox is active other than exiting and restarting Firefox.
I have encountered this problem a few times, so it's not just a freak occurrence. I have only experienced this with the Flash applet specified in the bug report, but I suspect that that's only because it's the only Flash applet I've seen crash the plugin in quite some time. The crash always seems to occur exactly when I ask it to fullscreen. I can't seem to recall whether it ever makes it to fullscreen or not when the crash occurs. If it does, it's only for a small fraction of a second. My suspicion is that there's a period of time where the menubar has been removed but Firefox is not yet aware it needs to restore it. This suspicion, and, in fact, this bug report itself, may be based on completely false notions of what application is actually in charge of making the menubar disappear and reappear. But the menubar says "Firefox" on it and not "Flash".
Here are some possibly-relevant "Console" logs: 8/5/14 7:06:36.706 PM WindowServer: disable_update_timeout: UI updates were forcibly disabled by application "Firefox Plugin Process" for over 1.00 seconds. Server has re-enabled them. 8/5/14 7:06:50.707 PM WindowServer: disable_update_likely_unbalanced: UI updates still disabled by application "Firefox Plugin Process" after 15.00 seconds (server forcibly re-enabled them after 1.00 seconds). Likely an unbalanced disableUpdate call. 8/5/14 7:07:45.535 PM plugin-container: CoreText performance note: Client called CTFontCreateWithName() using name "Times Roman" and got font with PostScript name "Times-Roman". For best performance, only use PostScript names when calling this API. 8/5/14 7:07:45.535 PM plugin-container: CoreText performance note: Set a breakpoint on CTFontLogSuboptimalRequest to debug. 8/5/14 7:08:07.384 PM plugin-container: CoreText performance note: Client called CTFontCreateWithName() using name "Lucida Grande" and got font with PostScript name "LucidaGrande". For best performance, only use PostScript names when calling this API. 8/5/14 8:20:27.189 PM Console: setPresentationOptions called with NSApplicationPresentationFullScreen when there is no visible fullscreen window; this call will be ignored.
I've found that I can reproduce the issue without relying on the plugin to crash by finding the Flash plugin-container PID, running "sleep 20 && kill <pid>", fullscreening the applet, and waiting for the signal to hit it. Oh, and I'm on OS X 10.9 (13A603).
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