Given that you’re not using a public computer and you trust your surroundings, pets and relatives, here’s a solution. No need to close Firefox, it’ll take the changes the next time you run it.

1) In the Directory_Where_you_installed_Firefox/components, find and open nsLoginManager.js in a text editor.

2) Search for “_isAutoCompleteDisabled” — without the quotes. You will find a block similar to the following code:

_isAutocompleteDisabled :  function (element) {
if (element && element.hasAttribute(“autocomplete”) &&
element.getAttribute(“autocomplete”).toLowerCase() == “off”)
return true;

return false;
},

You must add two forward slashes to comment out the second, third and fourth line, such as this:

_isAutocompleteDisabled :  function (element) {
// if (element && element.hasAttribute(“autocomplete”) &&
// element.getAttribute(“autocomplete”).toLowerCase() == “off”)
// return true;

return false;
},

Save the file, close your editor, restart your Firefox and you’re done!