Firefox is running in the process, but it doesn't show up in the applications tab in the task managers. Tried to start firefox in safemode as well, but failed also. Uninstalled and reinstalled, same problem. Latest add-on I have installed is zotero. I have seen warning message saying script file related to Chrome as well (chrome://browser/content/tabbrowser.xml:524) , but firefox would run after I stopped that script. Usually I run two browsers (chrome and firefox) simultaneously.