SVG and -moz-box-sizing do not interact well. The SVG "viewport" area should really be resized.
Clicking in the testcase toggles between 'content-edge' and 'padding-edge'. The circle should scale down when the value is 'padding-edge' instead of its right and bottom being clipped away.
Created attachment 593562 [details] testcase Testcase with 'viewBox' attribute. (The old testcase didn't have it, and so expecting scaling was wrong.) This testcase shows that box-sizing works fine.
(In reply to Jonathan Watt [:jwatt] from comment #4) > [...] This testcase shows that box-sizing works fine. Status: invalid?
Works fine for me, too.
A reftest regression test should be landed for this to be close. I'll write one next week if someone else doesn't do it first.
Removing dependency on bug 243412 (as we have no bug here, it shouldn't block dropping the -moz-prefix from box-sizing)