I upgraded this morning to the 0.1 version from 5.0.0, which I upgraded to yesterday. 5.0.1 downloaded fine, then I clicked on the install and reopen button (or whatever it says). That's when the system froze. I could only do a hard reboot. When the system came up, I had nothing on the desktop - no volumes or file/folders that are supposed to be on the desktop. File Finder was listed next to the Apple icon on the menu, but when I right-click on the desktop, I got no pop-up menu. I was able to open a Finder window and look around my files, all seem there, even the desktop folder in my home account with all the files contained in it. But nothing showed up on the desktop. When I click on the File Finder menu item, most menu items on the pull down menu are gray. I can close FF, but that does nothing on the desktop. I'm unable to open a FF finder window.

After repeated attempts to fix the system (reboot a number of times, try a few things in the system preferences), I gave up. I'm now restoring from a Time Machine backup. I should end up with FF 5.0.0 when done and hopefully I'll be back in business. I'll wait before upgrading to 5.0.1 and check MacFixIt for any bad reports.

BTW, the new version 5 has changed a few things in the finder window - it'll take a little getting used to. Over all, in the day that I used it before this problem, there were a few things that made the 5.0 worth getting. Like getting remote volumes in the left panel - that was a big one for me. The split finder window will be helpful at times.