This is machine specific. On a MacBookPro running OS 10.6.8 and Firefox 4.0.1 there are no problems. On a MacPro running the same OS and Firefox version, Firefox freezes on launch. Sometimes it will show a dropdown window, but frozen. It will open a window with the indication "Connecting", also frozen. The target home page is the same on both machines. Both machines are connected to the Internet thru the same router. Both can ping the same sites. There are no problems running Safari or Microsoft Explorer. Mac Disk Utility and Disk Warrior both show the disk on the desktop machine to be OK. The hardware test on the desktop machine came up clean. I cleaned all of the .mozilla files out of Libraries and put them on the desktop to try to force creation of new ones. The same problem occurred on the desktop machine when I had downloaded Firefox 5.0.1; I re-installed 4.0.1 in order to get a perfect parallel to the laptop setup. No cigar. Has anyone else had this problem? This _could_ be cookie related. My bank put some security login features on their website that were a pain in the neck, insisting that I was running from a public computer when in fact I was running from a Mac at home. Their staff suggested a workaround that would prevent their cookies from being deleted on logout. I tried that. It opened too many doors, so I went back to my earlier Preferences. Now I cannot get into the Preferences to look at the cookies. So I am running Safari in the interim, which hurts if you are a Firefox fan. Brings tears to my eyes (and makes me wash my mouth out with soap). Any advice would be much appreciated. Thanks.