User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.7; rv:13.0a1) Gecko/13.0a1 Firefox/13.0a1 Build ID: 20120218031156 Steps to reproduce: Create a new tab. Actual results: Spaces for thumbnails for frequently accessed pages are displayed, but the thumbnails are not. All thumbnails appear as blank grey with page labels beneath them. Expected results: Thumbnails contain thumbnails of pages.
Do you have any preferences which delete your memory cache at shutdown? or do you use it at all? that would be bug 724408 if true.
Fixed by bug 744388.