Flash player crashing, unresponsive, busy or stopped issue have been a real pain for FireFox user since Flash player version 11. Now it’s version 13+ and the problem still exists.
People have tried everything from reinstalling, downgrading, enable or disable functions, etc and none of them seems to work. From all the answers posted on online support forums, the only fix that actually work is by editing the Flash player .cfg file.
You can watch the YouTube video tutorial or you prefer reading the tutorial in written format.
More detailed steps if you run into permission issues editing the mms.cfg file:
1) In a My Computer or Windows Explorer window, open these folders:
For 64bit Windows:
Go to main C: drive â†’ Windows â†’ SysWOW64 â†’ Macromed â†’ Flash
If that folder does not exist, then you are using 32-bit Windows, and you can open the following folder instead:
For 32bit Windows:
Go to main C: drive â†’ Windows â†’ System32 â†’ Macromed â†’ Flash
(Note: This folder exists on both 32bit and 64bit Windows, but on 64-bit Windows Firefox uses the Flash player in the SysWOW64 folder instead)
2) Check for a file named mms.cfg:
a. If exists: drag it to your Documents folder where you can edit it without being bothered about administrator privileges.
b. If does not exist: open your Documents folder, right-click â†’ New â†’ Text File and name the new file “mms.cfg” (putting quotation marks around the file name help prevent Windows from tacking .txt onto the end).
3) Open mms.cfg from Documents into a text editor such as Notepad. Add ProtectedMode=0 anywhere in the line. I put it in the last line:
4) Save the file and close Notepad or text-editor.
5) Hold down the Ctrl key and drag the mms.cfg file back to the Flash folder to make a copy there, keeping the original file inside Documents folder.
This change should take effect the next time you exit and restart Firefox. Test it by watching YouTube or online streaming movie. Wait and see if the flash video player freezes or crashing FireFox.
Revert Shockwave Flash
6) Download flash “uninstaller” and uninstall currently installed flash player: http://helpx.adobe.com/flash-player/kb/uninstall-flash-player-windows.html
7) Download and install “Flash Player 11.7.700.242 (140.32 MB) (Released 9/10/2013)” from: http://helpx.adobe.com/flash-player/kb/archived-flash-player-versions.html
Hopefully this should work for you.