From the report, all of the crashes with this signature do not have much in common but the operating system and maybe graphics. This crashed while loading the silverlight plugin. Only add ons are disabled when you turn on Firefox with Safe Mode. However hardware acceleration is turned off.

In this case I would check your antivirus http://kb.mozillazine.org/Antivirus_software

Some added toolbar and anti-virus add-ons are known to cause Firefox issues. Disable All of them.

These programs were flagged;

kernelbase.dll = used for compatability purpose for older programs in windows 7

ntdll.dll = Microsoft

also; Process Type plugin Silverlight Plug-In

Perform a System File Check to fix the corrupted system files http://www.sevenforums.com/tutorials/1538-sfc-scannow-command-system-file-checker.html