After updating some extentions it recomeneded me to upgrade to 4 which I promptly did. After the upgrade a dialog box stated it was going to check extentions for compatability with the new version and almost instantly froze. I waited a few minutes and then force quit the application. I restarted my PC and launched FF. It did not nothing, I opened task manager and found that no applications were running BUT firefox did have a process going. I tried to launch FF in safe mode by typing firefox -safe-mode but it resulted in the same outcome :(