If you enable it on trunk, you get crashes in SVGImage trying to grab the DeviceOrientationClient, and it's not instantiated. Please fix :)
I believe this was fixed by Steve in Bug 43848. Please confirm if that's the case.
(In reply to comment #1) > I believe this was fixed by Steve in Bug 43848. Please confirm if that's the case. Yes, that will fix it. Apologies for the breakage. *** This bug has been marked as a duplicate of bug 43848 ***