I tried all the settings changes suggested here. Then I "refreshed" Firefox and I can now ask this question. Also, the gmail log-in would not proceed to password by "Next" after username.

Now I have lost my master password, although all my passwords have been preserved. It said it was unset but would not let me use the previous one. Is that usual? Also, of course, I have to re-install my add-ins. Is there a check for database corruption which could fix this sort of thing without "refresh" ?