build: Run test in Firefox by default (including locally)
build: Run test in Firefox by default (including locally)

Might as well. Runs quick enough, and I think it's as reasonable
to require Chrome to be installed locally as it is for Firefox.

Change-Id: I71e700a150b53baf6b6030bdd66f8402524bb006

wikimedia/oojs,wikimedia/oojs