Top level of Account Levels "doesn't take" (bug2069949)

The issue is that the text I type into the top level of account settings, which has Account Name, and Default Identity, '''doesn't save'''. Initially I entered the email address and Thunderbird found the correct details, but I was creating seven new accounts and was going to come back later and fill in the details. However, the details on this page don't stick, wand it reverts to blank entries (as shown in the attached image), and each account's name defaults to the email address. It's awkward because if I create a new message it won't add a signature because that gets cleared with the other details on this page. This might be related to an earlier question I asked [[Delete Account button doesn't work.]] since it's on the same page as the DELETE button. This suggests to me that there's a script engine that I'm missing on my PC. This is only a guess. I use Fire Fox as my main browser, and Vivaldi as a backup. As I say, this is only a guess.