Following initial reports of the problem from users, Mozilla issued an update for Firefox, version 13.0.1, to fix the problem. However, some users continued to experience crashing issues when viewing Flash content with Protected Mode enabled. The new 11.3.300.262 release of the Flash Player plugin should now resolve this. According to the release notes, there is, however, a known issue that causes audio distortion when streaming some Flash content.
Existing users with the built-in background updater for Windows enabled should automatically be upgraded to the new release. Alternatively, Flash Player 11.3.300.262 is available to download from get.adobe.com/flashplayer/.