Sorry for flooding the newsgroup and mailboxes. I've used Google Groups web interface and noticed the disaster later.
Anyway, I talked to fallen and he agreed this is a bug. I wanted to add it to Bugzilla but I've found some issues which always report something but the root of the problem is what wrote above. One <
https://bugzilla.mozilla.org/show_bug.cgi?id=459683> is still open. I hope we'll be able to find some resources to fix it soon, but it can't promise anything.