Have you checked your firewall rules? With a rules-based firewall, you have to allow Firefox to communicate with itself using TCP on the localhost address.

I don't know what you mean by using TCP, but my firewall allows Firefox. I still have to use IE to access anything that requires signing in.

Is there any way to switch back to Firefox 7. My sister has it and has no security problems with it.

I have decided to uninstall Firefox and use IE even though I don't like it as well. The link from the notification email didn't even work. It is hopeless.

Firefox 10 and Thunderbird 10 both seem to behave differently with firewalls. It is a big advantage to have a firewall that will ask what to do if it has no rule to cover a situation. Mine asked me if Firefox was permitted to use port 443 (https).