An extension is the most likely cause of this problem - try starting in Firefox Safe Mode to see if this is the case. See [[Safe Mode]] for instructions. You may need to end Firefox's process in Task Manager: # Press '''CTRL+SHIFT+ESC''' to load the Task Manager window # Click the Processes tab at the top. (Click once near the top of the window if you don't see tabs) # Find all '''firefox.exe''' processes listed below # On each firefox.exe process, right click and choose '''End Process''' If it starts in safe mode, disable extensions to figure out which is causing it. Norton IPS and Norton Toolbar are known to cause it in some cases, so disable these first.