I'm developing a Firefox plugin that needs to be able to temporarily disable all types of autofill. Both the case where the fields come immediately pre-filled and the case where it suggests data for you when you start typing. I can turn off the gathering of new form data using the Firefox settings, but the form data that's already saved is still used.
Note that I don't have control over the sites being displayed, so autofill = false doesn't work. By the time I get access to the page, Firefox has already helpfully filled in the form data.