For tiles not to suck, we need to start aligning our display port with tile boundaries. We have various display port strategies in fennec, we should probably port our default one to native.
Also you'll probably have to port the wonderful wonderful code at https://hg.mozilla.org/mozilla-central/file/8196c86355bc/mobile/android/chrome/content/browser.js#l2988
Going to start looking at this.
I've decided to split this into another bug (bug 907743) - We should still consider this because I suspect that the Android display-port code is better and better-tested, but it's really the tile alignment that we need on b2g more than the algorithms themselves (which is a larger piece of work).
We have a bunch of displayport strategies in APZC now as well, which are controllable by various prefs and combinations of prefs. I don't think there's much value in pulling over the rest of the strategies from Fennec, mostly because we've really only ever used one of them even on Fennec and that's the approach we're also using in APZC. I'm going to close this bug but feel free to argue otherwise.