Firefox will neither load, uninstall or upgrade, due to a Firefox running message, when it isn't.
I have just installed the program. It won't start. I tried to uninstall; however, a message came up that it wouldn't uninstall while running. Windows xp says it is not running. The same message appeared when attempting instead to upgrade.
Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; Comcast Install 1.0; Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1) ; .NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR 3.0.04506.648; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729; BO1IE8_v1;ENUS)
Do a clean reinstall and download a fresh Firefox copy from http://www.mozilla.com/firefox/all.html and save the file to the desktop. Uninstall your current Firefox version and remove the Firefox program folder before installing that copy of the Firefox installer. It is important to delete the Firefox program folder to remove all the files and make sure that there are no problems with files that were leftover after uninstalling.
You can skip the step to create a new profile, that is not necessary for this issue. ..... See http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Clean_reinstall