i also found this if it's just firefox that crashes with the new flashplayer 11.3.300.265
If this update does not fix the crashes, try following Adobe’s advice from the last version – “for users who cannot update to Flash Player 11.3.300.257
Adobe has developed a patched version of Flash Player 10.x – Flash Player 10.3.183.20, which can be downloaded here.”
http://helpx.adobe.com/flash-player/kb/archived-flash-player-versions.html
‘Patched’ means that it has all the most recent security updates so is safe to use, albeit without the new features of version 11. (Old versions of 11.3 or 11.2
are not safe to use as they do not have the latest security updates).
The link leads to archived versions for developers. Scroll down to the ‘Release and Content Debugger Archives’ and download the 10.3.183.20 zip archive then close Firefox.
Unzip the archive and browse to the 10.3.183.20 folder then run the uninstall_flash_player_win.exe utility to remove the current faulty Flash 11.3 version.
Now install Flash for Firefox – the file is named flashplayer10_3r183_20_win.exe
Hopefully a future update will fix version 11.3 at some point but for now version 10.3 is up to date and works ok…