As I add and depend on more restyle hints (in particular eRestyle_CSSAnimations and eRestyle_CSSTransitions added in bug 996796), I want to use those restyle hints on everything that transitions and animations can run on. Unfortunately, right now, we can't send restyle hints directly to ::before or ::after pseudo-elements, even though we do have a DOM node representing these pseudo-elements. I'd like to try to make that possible in this bug; I believe it would simplify a bunch of things (and also, eventually, make it easier to support OMT Animations on these pseudo-elements). I don't think this requires preserving the pseudo-element DOM nodes across reframes since a reframe wipes away the need for other restyling, although it might also be useful to do that at some point (similar to what I did for style contexts in bug 625289.

Actually, I think this might just work, but I was confused because of some code that I misunderstood when naming methods in https://hg.mozilla.org/mozilla-central/rev/95ec9086d91a .

I filed bug 1057098 to fix that naming confusion.

Seems to have just worked.