A very handy thing. Unlike automatic form fillers, does exactly what is needed. Useful for filling name, email, address or similar fields, avoiding typing mistakes. With the autocomplete feature, became much more handy.
So handy and simple. Name, address, email addresses and postcode, or whatever, are just a right click away. Go to your Add ons, Extensions, select options in Simple Form Fill, and find the edit button down the bottom so you can fill in your stuff.
I've been using the old "FormFiller" add-on for years, which was not officially supported any longer but still working OK on latest Firefox builds if you tweaked its version compatibility.
However, this add-on not only does what FormFiller offered (i.e., context-menu selection for form field values) but the editing interface for those values is extremely fast and easy to use. I've since dropped the legacy add-on and moved to this one, which is greatly appreciated.