I thought I'd try and start a discussion about this bug on the newsgroups. I'm very opposed to 'fixing' this bug because whether or not it's defaulted to off it will still encourage people to have bad habits and the last thing I want to do is encourage more people with sigs above the quoted message.
The current reasons for/against this feature are commented in the bug. My main argument against it is that it ruins readability, reading a top posted thread is more difficult anyway, never mind adding a huge corporate sig before the quoted text. Personally I'd want to see this bug marked wontfix, if people really want to add the quoted text after the sig, I'd rather see bug 70478 - http://bugzilla.mozilla.org/show_bug.cgi?id=70478 - fixed because then the user can turn off quoting text automatically and then paste the quoted message wherever they deem most appropriate.
