This is a potential fix for ticket 8763 (marked "cantfix" right now). Basically, I'm going with the assumption that WebKit Bug 13343 and Mozilla Bug 548397 are mutually exclusive. So if you are affected by the Mozilla bug, then you know that you have a reliable margin-right implementation.
Potential fix for #8763
Hard to argue with that logic ... :)
Agreed. Really hard to imagine Mozilla getting a bug that's already been fixed by webkit and needing to work around it in a supported browser.
Landed in commit 304dd61.
Landing pull request 370. Fixes #8763.