DPC3939B port forwarding broken in edge browser

If you discover that port forwarding seems completely broken, i.e hitting save on the edit or create port forward screen just ignores you, then try a different browser.

It seems the new chrome based edge browser is not supported and the save button seemingly has no effect.

Switching to internet explorer shows a status bar while saving, which presumably blocks it  working under edge. (disabling the popup blocker for this IP address seems to have no effect)