When navigating the password manager doorhanger autocomplete suggestions via keyboard, pressing 'enter' should select the currently focused suggestion, fill it into the input, close the popup, and make no other changes. Currently all of the above happens, but the doorhanger is saved/updated as well. This makes it difficult to select values via the keyboard, making this an important accessibility problem.
Additional acceptance criterion: the patch that fixes this should also update
browser_doorhanger_submit_telemetry.js to select suggestions using the keyboard (instead of
EventUtils.synthesizeMouseAtCenter), and remove
skipif linux from that test.