stabilize firefox test runner to use cfx run.

This stabilizes the firefox test tooling for our integration test.  That is now stable despite the latest firefox, but doesn't change underlying tests.

It gets oAuth to pass more but it still seems flaky
rtcpeerconnection is failing
social integration double is timing out sometimes. (flaky)

It was nice for me to be able to switch in and out that comment to make sure the test setup worked as expected and that I knew what this function was actually doing.