The requested URL /forum/ was not found on this server. <---- I get this when I am in firefox. I go to explorer and I can get in.
Sometimes, shortened URLs cause havoc with Firefox. There's an easy fix around this, though.
Open a tab, and in the address bar type: about:config
You'll get a neat, humorous warning. We're cool, just say you understand and get to the configuration screen.
Now, look for a line that says: browser.urlbar.trimURLs
You'll see it's most likely set to true. Double click that line and it should read false. Close the tab and try again. Fixed?