I just looked more into this: http://www.w3.org/TR/CSS2/box.html#margin-properties "The percentage is calculated with respect to the width of the generated box's containing block. This is true for 'margin-top' and 'margin-bottom', except in the page context, where percentages refer to page box height." I guess that's the way it's supposed to be . . . (looked at IE7 as well, and it's the same with them). Appologies for the bug report about a non-bug. I still think this is foolish . . . guess I should take that up with the W3C.
(In reply to comment #1) > I just looked more into this: > > http://www.w3.org/TR/CSS2/box.html#margin-properties And CSS2.1 is possibly more clear http://www.w3.org/TR/CSS21/box.html#propdef-margin Gecko's behaviour is correct.