The last firefox update was specifically for Flash and silverlite, they run in external processes and will not competely shut down firefox in the event of a crash.
"Results from our beta testing show Firefox 3.6.4 will significantly reduce the number of Firefox crashes experienced by users who are watching online videos or playing games," Mozilla'* Mike Beltzner wrote in the official Mozilla blog. "When a plugin crashes or freezes while using Firefox, users can enjoy uninterrupted browsing by simply refreshing the page."
I don't think it'* a cut and dry plug-in issue since I have reinstalled flash, I may set the timeout value higher for now, or see how chrome has matured.
"Going Off the Rails On the Swayzie Train"