the scoped mixin no longer depends on it directly

It has new API which we want to use.

Newest Ubuntu switched Firefox to a snap, which breaks karma.

Try to use playwright to download and cache firefox/chromium
and use those for karma.

Compared to puppeteer where we did this some time ago this caches
the browsers globally, and only downloads them when we start the tests.

This now lives in the checkin topic, its only user.

This reverts commit 6c632dc6