It's as simple as possible but no simpler (with apologies).
There are no words to express how helpful this add-on is.
The only problems I've found are of my creation!

Simple to set up. Simple to use. Perfect! Just what I was looking for. Can set up any string of characters to be saved in the add-on for use on any form.

hallo.
ist gut.

Hi,
Thanks for reply, but you are taking it wrong.

I am asking you to provide an option of completely remove 'Simple Form Fill' from the context menu (not a single item):
https://addons.cdn.mozilla.net/user-media/previews/full/184/184694.png

Currently this is visible even if you right-click on empty element of any website.

Nothing fancy like the form fill feature of LastPass but it does it's job albeit not as quickly.