so has there been anything more on this? I'm having almost the same problem. Sessions aren't saving; I get the right number of tabs but no websites for them. I've double-checked TMP settings, Remember History is set, I did the whole uninstall/reinstall my extensions, I followed directions for the error console and about:config. I don't have the .NET add on that gave ppl problems. And I still have no reason for the empty sessions. The alternate profile was chugging along fine, I switched back to the old one to see if dumping my Personas themes would help (didn't), switched back to troubleshoot and the new profile crapped out. And this was after several restarts with the reinstalled extensions. The only thing that's working is to set each browsing session as my Home Page before I close FF.
My info:
Windows 7 Home Premium (just updated w/SP1, prob pre-existing)
Firefox 4.0.1
TMP 0.3.8.5
My Ext:
Application: Firefox 4.0.1 (20110413222027)
Operating System: WINNT (x86-msvc)
+ All-in-One Sidebar 0.7.13
+ AutoPager 0.6.2.8
+ avast! WebRep 20110101 (Disabled)
+ Download Statusbar 0.9.8
+ Echofon 1.9.7.3
+ Evernote Web Clipper 4.0.0.138228
+ Extension List Dumper 1.15.0
+ Fast Dial 3.4
+ Fire.fm 1.4.14
+ Gmail Manager 0.6.4.1
+ Google Shortcuts 2.1.6
+ Greasemonkey 0.9.2
+ Integrated Gmail 2.6.18
+ Java Console 6.0.24
+ Java Console 6.0.22
+ LastPass 1.72.0
+ Simple Timer + Clocks 1.3.3
+ Skype extension 5.2.0.7165 (Disabled)
+ Stylish 1.1.2
+ Tab Mix Plus 0.3.8.5
+ TinyURL Generator 2.5.0