(Keep in mind this is on OSX Snow Leopard)
I don’t know how to describe this bizarre issue very well or even if this is the right place to do so, but out of nowhere Firefox locked me out of a login session on a dev site on my localhost. I was saving some data and I was redirected to the login page. I tried to login and it failed…and failed…and failed some more.
I checked the login PHP script and it reports a match for the username and password, but for some reason I can’t actually log in. I feel as though the session is being automatically deleted right after it gets created. I tried restarting the browser, then my computer. Nothing. I downgraded back to Firefox 12, no cigar. I tried clearing my cache and cookies, same thing.
I attempted to login with Safari and it was successful! Same with Chrome. So the problem is clearly Firefox. Could it be that my Firefox installation was corrupted and that simply installing over it with an older version won’t do anything? That I’ll have to completely remove it and then install it? I am seriously at my wit’s end here.
UPDATE:
After creating a new Firefox profile in Firefox 12 I was able to login (but only with the new profile). I then re-updated to Firefox 13 and was also able to successfully login (again, only with the new profile).
It then occurred to me that there must be something wrong with the domain (within the Firefox profile data I’m assuming). I created a domain alias and used that to login using the corrupted profile and it worked! So, I’ve narrowed it down to the domain and the profile. Maybe that will help.
Since you’ve narrowed it down to having something to do with your profile, try removing items from your problematic profile one at a time, to pin-point the problematic/corrupted file in the profile.
Since you’re on a MAC, your profile should be in one of these two locations:
~/Library/Mozilla/Firefox/Profiles/
~/Library/Application Support/Firefox/Profiles/
(Source: Here)
Here are some other links that may prove useful: