Adobe Flash crashes in Firefox

The pulsating menu is the interesting symptom, and probably doesn't have anything to do with us.

My guess is that it's a stuck key... this should fix it:

• unplug your keyboard
• run your hand vigorously back and forth across all of the keys a few times.  Make sure you get all the weird ones.
• flip it over and give if a few thumps on the back and shake it a bunch to get any remaining traces of last thursday's sandwich out
• plug it back in

If that doesn't work, I'd love to see a screen capture of the flickering menu.  Also, this would be a great time to reboot (actually power the machine and everything attached down for a minute and then power it back up), to see if the flickering persists.  If it does persist, you might try again with the bare minimum of stuff plugged in - mouse/keyboard, or nothing if it's a laptop (and if it's a laptop, check the laptop keyboard too...)

Also, if you're not using 64-bit Firefox (it's not the one you get by default under most circumstances), I would highly recommend switching.  The 64-bit variant includes a native NPAPI sandbox for Flash Player (older versions of Firefox lacked effective plug-in sandboxing, so we tacked our own sandbox on, but it's inherently inefficient because of the necessary architecture), and it solves the majority of the general stability problems.

My guess here is that you've got a stuck key, and it's generating a large number of input events.  This is what's causing the menu in the browser application itself to flicker.  The architectural inefficiencies that I described are characterized by messages between Flash Player and Firefox becoming so numerous that they overwhelm the operating system and either don't all get delivered or they arrive out of order, such that Flash Player or Firefox will hang waiting on a response that will never come.  Sticky key sending tons of input events between Flash and Firefox increases the likeliness that you're going to hit that hang.

So, in short:

- Performing some rough keyboard hygiene should get the offending key unstuck, unless there's liquid in it (it could also be a freaked out USB device or something)

- Moving to the 64-bit variant of Firefox resolves the fundamental sandbox problem. Get the one from the x64 column.
   Mozilla Firefox Web Browser — Download Firefox in your language — Mozilla​

If those things don't help, a crash report from the 64-bit Firefox would be helpful.  The 32-bit crash report will probably just be the standard generic hang described above, but I'm happy to confirm.

Please see the following guide on how to report a crash or error:
https://helpx.adobe.com/flash-player/kb/report-flash-player-crash.html