Tableview, your experiences seem to be even worse than mine! I've been using Thunderbird with total satisfaction until relatively recently when there was a flurry of updates and, rightly or wrongly, I've put the new problems down to this.
I have just repeated the above exercise with the prefs file in my Thunderbird profile, only this time I deleted the earlier renamed prefs.OLD version first and then renamed the prefs.
js file in the active profile in my computer's user account and did the same to the prefs file (no .
js version here) in the unused profile in my admin account. To momentary alarm (!) I found that all of my e-mails had disappeared again so I restored my profile, with the
exception of "Settings", with MozBackup. Everything appeared to go well. When I opened the active Thunderbird I expected to have to reset all of the account settings because I had elected not to restore them (or so I thought) but, no.... they were there exactly as before and also as before, all attempts to change them were ignored. Bl***y stupid program! How can this be?