Hi there John! Thanks for going public with this. :)
You should be able to toggle the preference using
browser.formfill.enable by putting that in a file, on a URL, and using
that with prefs= API.
E.g. prefs=
http://prefs.webconverger.com/2014/eg.js
I don't have time to test this today.
But but, you should really be just closing the last tab and resetting
the session between different users though?
Happy holidays,