Sometimes you just really want to use the autocomplete feature and omit the HTML form autocomplete=”off”.

To do so, you need to modify following file (the firefox version might, and probably will be, different than the one posted below):

/usr/lib/firefox-3.6.10/components/nsLoginManager.js (in Windows it might be something like C:\Program Files\Mozilla Firefox\components\nsLoginManager.js)

Change this:

_isAutocompleteDisabled :  function (element) {
    if (element.getAttribute("autocomplete").toLowerCase() == "off")
        return true;
    return false;
}

to this:

_isAutocompleteDisabled :  function (element) {
    return false;
}

Or just add comments to the conditional section of the method, to assure it will always return false.