Allow user to try different credentials when saving entry on all SPAs

[luckyrat]

Single Page Applications that do not create a new form after a failed sign-in attempt will lose their submit listener so further attempts by the user to type and then save their correct credentials will only work if they refresh the page between each failed attempt.

Not sure what we can do about this without risking leaving listeners lying around taking up memory.

Maybe some sort of timeout could help? If the submit button still exists after a second we can reattach? Seems flaky. Needs detailed planning. Ideas welcome.

[luckyrat]

Firefox's solution might be worth investigation, although whether it is possible to replicate that approach from within a webextension is doubtful: https://bugzilla.mozilla.org/show_bug.cgi?id=1166995