I've noticed with Firefox (17 ESR) that, having once used Firebug to delete the 'autocomplete="no"' attribute on a password field and then submitted the form, it's not necessary to do so again; in whatever heuristic Firefox uses to determine how to behave in that case, the existence of auto-completion data for the field apparently overrides the advice given by the attribute. For those leery of adding still more extensions to a Firefox profile already well larded with them, this may be useful information.