Does it say "Not responding"? I'd try reinstalling firefox. I've had this problem before and by reinstalling firefox, it fixed the problem.

If you have submitted crash reports then please post the IDs of one or more recent crash reports that have a "bp-" prefix: *bp-xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx You can find the IDs of the submitted crash reports on the <i>about:crashes</i> page. *You can open the <b>about:crashes</b> page via the location bar, like you open a website, or open the crash reports page via "Help > Troubleshooting Information". See: *http://kb.mozillazine.org/Mozilla_Crash_Reporter *https://support.mozilla.org/kb/Mozilla+Crash+Reporter If you can't open Firefox, see: *http://kb.mozillazine.org/Mozilla_Crash_Reporter#Location_of_crash_reports *http://kb.mozillazine.org/Mozilla_Crash_Reporter#Viewing_crash_reports *https://developer.mozilla.org/How_to_get_a_stacktrace_for_a_bug_report