Firefox: disable autofill in forms

For some reason they don't make this so straightforward any more.

Just go to about:config and set

browser.formfill.enable = false
browser.formfill.expire_days = 1
services.sync.prefs.sync.browser.formfill.enable = false

There's a suggestion that setting browser.formfill.expre_days to 0 is more secure for expiring existing saved data, however 0 often means never expire. Without looking at the code, I'm just going to err on the (to my mind) safer bet of setting it at 1.