This feature relies mostly on a search predicate key we did not support.
With that added we at least get some functionality although you encounter
bugs pretty quickly. For example a button after a password field loses focus,
but this seems to be a bug in Safari too. I think the browser support here in general
is pretty underwhelming at this time.
Note: This just works because we now start a11y when a role is retrieved, so
we don't need to sniff out any special FKA settings.
Differential Revision: https://phabricator.services.mozilla.com/D219822
642922bc35