I just upgraded and now Firefox will not even open!!

What happens when you try to start Firefox? Some things that might be relevant depending on the answer... Sometimes Firefox will "hang" during startup. The process is in memory but stops working. In that case, you may need to use the Windows Task Manager to "kill" the process. * You can launch the Windows task manager by pressing Ctrl+Shift+Esc. * First check the Applications tab, then check the Processes tab (look for firefox.exe). * You can select the stalled item and use the End Task or End Process button. Note that if Firefox actually were in use, this could cause data loss, but since it's not yet displayed, this should be okay. Sometimes a program-control firewall will block an upgraded Firefox as possibly being modified by malware. In these cases, it may help to clear any references to Firefox from the firewall and have it redetect the application when you try to start it.