Comment 338 for bug 195698

The basic cause of this (and all the similar related bugs) is that there was never any code to explicitly check/prevent multiple prompts. Things just relied on the prompt blocking *everything* (ie, one tab prompts for something, every other tab freezes). Thus you'd only get one prompt at a time, and that also prevented getting repeated prompts for the same login.

Thread manager came along in 1.9, removed the blocking behavior (highly desirable for other reasons), and no one realized the complexity of the problem until it was too late to safely deal with it.

Multiple master-password prompts are one symptom of this problem, and could perhaps be wallpapered over by forcing a prompt before anything starts loading... Except that would mean you'd *always* get a MP prompt, even if the restored session wouldn't normally need to prompt. Such wallpaper also wouldn't help with the specific flavor of this bug, in that you'd still get multiple prompts for the same HTTP auth (and proxy auth).