This one seems to be the opposite of what I would expect. As SharePoint Administrators, we’ve all advised our users not to use "unsupported" browsers like FireFox. But I ran across an issue today where someone had been using FireFox to open the company’s intranet site for several months because when they tried to open it with Internet Explorer (8), an error was displayed: Internet Explorer cannot display the webpage.
Solution: After finding out that the user wasn’t even being prompted for credentials – the site uses Windows authentication – I asked them to reset their IE settings by going to IE -> Internet Options -> Advanced -> Reset Internet Explorer Settings. And that solved the issue.
In searching on the web, I found several other ideas and tried a few but we didn’t have success until the IE settings were reset to their defaults.