You can adjust signature placement here: '''[http://kb.mozillazine.org/Menu_differences_in_Windows,_Linux,_and_Mac Tools|Account Settings]|<select account>|'''Composition & Addressing You can also set it to not attach the signature when replying, which might be enough for your needs. I've not heard of it "truncating" before. The default placement suits newsgroups, where sigs are added at the bottom, and anything below the first sig can be automatically trimmed when quoted or replied to. For this to work, a standardized marker is required to indicate where trimming can take place, and that's the "-- " delimiter. So, in that environment, anything below "-- " could and may be removed subsequently. If you use the delimiter at the top, then there's a risk that all the quoted material below your own signature could get lost. Given that all I've said above is about newsgroups, its relevance to email is somewhat dubious. Many users who have come from Outlook and other MS email clients seem to hate the "-- " with a passion and want rid of it. It can be easily removed via the config editor. http://kb.mozillazine.org/Signatures_%28Thunderbird%29#Removing_the_signature_separator People who top-post don't like or see any use for the "-- " and I have some sympathy with that viewpoint. Those who bottom-post or interleave tend to understand the value and usefulness of the signature delimiter. But there's no point being dogmatic about replying style; the only good way to do it is to comply with the precedent. And since most people only top-post, that's what we become stuck with, and "-- " becomes redundant.