Updated to Firefox 6, see first post for details I think I've found the reason for this bug. Expect some information in the next few days on KernelEx' bugtracker. I don't have that much time at the moment, sorry. Short version: UnlockFileEx unimplemented(easy to fix), region locks affect file mappings to everyone, even the creator(in case anyone wants to take a look at it). I haven't looked at the bookmark and history issues yet, but I can absolutely confirm them. Maybe there will be also a Seamonkey 2.2 build for 9x soon if no unexpected problems show up.