where did mail.dll go in Portable TB 1.5?

Does anyone know where the mail.dll went in Portable TB 1.5? I really want to remove the annoying "-- " divider TB places above all signature.

The topic on mozillazine dating back to Aug 03 display a solution by editing the mail.dll file, however i can't seem to find it. Below is a direct quote from the topic

You can get rid of that if you edit file mail.dll. Change "-- " to " " (three blanks) on ONE place.

I've posted same question on mozillazine, but no response, andy ideas?