I am trying to modify my e-mail signature. I can change it under Account Settings, and it will work as such until I quit TB and restart it, whereupon it reverts to the original signature. The same thing is true for settings to add the signature on forwarding or replying to a msg. I've tried changing the signature in plain text and in HTML in the dialog box, and also saving it as an HTML file and checking the "Use HTML" box. I think this might have something to do with migrating my Thunderbird profile to a new M1 MacBook Air from a backup of an account on my old Intel MacBook Pro. I doubt it has anything to do with the change in processor, but suspect something (perhaps the prefs.js file) got corrupted, or had its permissions messed up, in the migration, and I don't know how to reset it/them. Tabs also are not saved between sessions of TB, and tabs don't work properly - e.g, sometimes the last tab will replace all the previous ones (so as one closes the last tab, the one to the left of it gets written over by what the last tab referenced, and this continues with closing each tab). I don't know if this problem is related. I tried deleting "session.json" as suggested by someone (but not session.json.backup), and it does not solve the tabs issue. Any help will be greatly appreciated, thanks!