Your crashreport is:
https://crash-stats.mozilla.com/report/index/bp-6922f9fd-7667-4115-a32f-1a9632111103
Firefox 7.0.1 Crash Report [@ _purecall | nsXPTCStubBase::QueryInterface(nsID const&, void**) ]
This may be related to a program called Trusteer Rapport. Which version (build ID) of Rapport do you have? If you disable it, does the crashing stop?

3.5.1108.52 is the version of Rapport. to be honest i have just uninstalled and re installed firefox but now i have had to remove all my user data, this has allowed me to use it again, Rapport is currently not affecting the program, but i will probably remove it anyway, thanks for your help! :)