It seems to generate an effectively unbounded number of copies of my address, some correct and some wrong. The UI to manage it is hidden and very minimal. The obvious options like telling the autofill my address once, correctly, and with no further automatic guesses are absent.
My general assumption is that, if I let Firefox autofill my address, it will insert portions of my address into various fields at random, biased somewhat but not very strongly toward getting them in the right place.
The autofill feature that tries to autofill things like shipping addresses. As far as I know, it’s entirely unrelated to the username/password autofill feature.
