I have this problem as well. Hotmail just opens fine, but it won't allow me to click on any of my emails. If you click on any email, (or junk/deleted folders etc.) it almost seems as if it is "locked", and nothing will happen.

I had the exact same problem, and I found a fix for it, but it may not be what a lot of people want to hear... You need to upgrade to Firefox 4.01. I know, it kinda sucks, but it fixed the problem for me.

The BEST way to do this (and maintain all of your bookmarks/services intact) is to go to Help >> Check for Updates. This process will perform a search for the update, and allow you to upgrade to 4.01 -- not a complete re-install -- and this will maintain all of your existing "stuff" from 3.6.x. Only downfall I ran in to with this is that the "Wikipedia Toolbar" service (that I use quite often for work) isn't supported. Bummer, but I'd rather have access to my Hotmail account, and just set up a bookmark for Wikipedia.

Anyway, hope this helps, and good luck!

Hotmail is rolling out a server change at their end which might be causing this problem. Mozilla has spoken to them about it and they are trying to fix it. I won't be able to provide you a time estimate by when it will be solved but hotmail/mozilla is certainly looking at this issue.

I will let you know if get any updates!