Add Firefox versions for api.MouseEvent.region (#16938)
Add Firefox versions for api.MouseEvent.region (#16938)

* Add Firefox versions for api.MouseEvent.region

This PR adds real values for Firefox and Firefox Android for the `region` member of the `MouseEvent` API, based upon results from the [mdn-bcd-collector](https://mdn-bcd-collector.appspot.com) project (v6.0.8).

Tests Used: https://mdn-bcd-collector.appspot.com/tests/api/MouseEvent/region

_Check out the [collector's guide on how to review this PR](https://github.com/foolip/mdn-bcd-collector#reviewing-bcd-changes)._

* Remove irrelevant flag data
chrisdavidmills/browser-compat-data,chrisdavidmills/browser-compat-data,mdn/browser-compat-data,mdn/browser-compat-data