On b2g devices, http://people.mozilla.org/~mwoodrow/dz-broke-transforms.html used to have the game scaled to fit the iframe. It is now too big. This may be related to us changing the UA string.
In a gecko build from a week ago or so, the games were served at 320x480. Now they're served at something like 4x those dimensions. Changing the UA string seems a likely cause of this. We may need to morph this into an evang bug.
Note that we have since update the CSS in Gaia: https://github.com/mozilla-b2g/gaia/issues/3325
We're working around this, but the games are drawing 16x more pixels than they were before, so performance has gone down the toilet.