Now, for fixes that don't alter the main mozilla files:
browser/installer/package-manifest.in : Add @BINPATH@/components/telemtry.xpt right after @BINPATH@/components/zipwriter.xpt (updated in mozilla 7.0)
browser/app/profile/firefox.js: Replace max_concurrent_tabs, 3 with restore_on_demand, true (updated in mozilla 7.0)
With these fixes, the sessions should restore just fine. I'm continuing to go through and figure out what has changed since 6.0. I'm going on the assumption that the files were correct at 6.0, considering that that's what the subversion says.