Hi Gareth,

Good point. Yuren and I thought about that.

But if we use the manifest/blacklist feature for this situation,
we should support multiple manifests at one time in https://github.com/mozilla-b2g/marionette-js-runner/blob/master/bin/marionette-mocha#L83 first.
Then we could handle different situation with the blacklist feature, like blacklist for some app features, blacklist in local, blacklist on Travis, blacklist on TBPL.

Before the multiple manifests happen, I think we could use the above solution first.
It is simple and easy for current situation.