Did you try a clean install of FF? If not please do so to see if the update may be went astray. Before clean installing FF do a back up of FF settings. When uninstalling FF let it delete all settings.
But we may also be looking at hardware or driver problem in the background as well because of the reboots.
Download Bluescreenview and check the Bug check string and Bug check code from the last three crashes if available and report them here.
Firefox should not get sandboxed by the automatic sandbox because it is a safe application. You can take a look in View Active Processes in Defense+ to see if it gets sandboxed. Or otherwise check under Computer Security Policy → Always sandbox to see if you manually have it running in the sandbox.