Before when I was having problems, i checked out the forum via ie, and i think ie logged in ok, but then later MFF logged in, too, though occasionally having login issues. But, on a daily basis, I'm using Firefox:
Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.9.0.1) Gecko/2008070208 Firefox/3.0.1
and with NoScript running, and with AVG firewall settings in place. I a few weeks ago was experiencing login issues, but not to day nor yesterday, and i don't think during last Monday thru Wednesday, either.
(I just started using NoScript yesterday, due to hearing about a new Flash exploit in which the clipboard cache is hijacked, the machine locked, and sensitive contents sold off or misused...
http://blogs.zdnet.com/security/?p=1733So, unless you have total confidence in your system security, all might wan to be mindful of what is collected by Ctrl+C, such as passwords, intranet URLs, external sites... )
But, back to the subject, could it be your home or corporate firewall settings?