I have a bunch of prefs-####.js files in my profile folder (as well as one prefs.js dated now). I'm not sure if I need all of these, as the knowledge base is not clear: " It only stores changes made to the defaults, after they are written back to disk. This normally occurs when you exit the Mozilla-based application."

This makes it sound as though each file only has changes, which would be silly for TB to have to go through all of these. And it seems it writes a new file every time it gets mail or I write mail.