Clear the cache and the cookies from sites that cause problems.

"Clear the Cache":

• Tools > Options > Advanced > Network > Offline Storage (Cache): "Clear Now"

"Remove the Cookies" from sites causing problems:

• Tools > Options > Privacy > Cookies: "Show Cookies"

Thank you for your reply, but this did not solve the problem.

If clearing the cookies doesn't help then it is possible that the file cookies.sqlite that stores the cookies is corrupted.

Rename (or delete) cookies.sqlite (cookies.sqlite.old) and delete cookies.sqlite-journal and cookies.txt, if they exist, in the Profile Folder in case the file cookies.sqlite got corrupted.

Thank you again for your help. After clearing the cache and cookies, and still having the problem, I uninstalled/reinstalled firefox. I had tried this before, but allowed it to keep my bookmarks, etc.. This time I had it remove everything (this is a check-box when doing the uninstall).

After reinstalling Firefox this time, the problem went away. Thank you for your help. Your comment about the cache and cookies, made me think that removing all information during the uninstall would help, and it did.

I don't know if your second suggestion would have helped, because it is now fixed. But I believe it was a possibility.