I just experienced an issue with Firefox 5 on Windows 7 where I could no longer navigate Hotmail.
Clicking on emails did nothing and clicking on mail folders also did nothing. Quite a few people seemed to be experiencing the issue and the fix for me was to simply clear the Firefox cache:
Click the Firefox button at the top left and then click Options and then Options again.Click Advanced followed by the Network tab and then click the Clear Now button to clear the offline cache. Restart Firefox.