Firefox extension for loading and saving webform data?

[Adam Funk]

There's a longwinded webform that I occasionally need to fill in, but
sometime when I click submit I get a 501, and then the back button
takes me to an empty form to fill in again.

Years ago I had a Firefox extension that added "load" and "save"
options to webforms, so you could save a partially or completely
filled-in form as a flat file on disk and reload it
later. Unfortunately it has disappeared (probably from lack of
maintenance and obsolescence).

Does anyone know of such a thing that works on the current version of
Firefox?

Thanks