Test-case: data:text/html,<!doctype html> <body style="font-size:25px;-moz-transform:translate(1em,1em);overflow:hidden"> <div style="height:100px;width:100px;background:blue; -moz-transform:inherit;font-size:100px"></div> In Chrome 19 dev, the box is offset by only 50px. In Gecko, as well as IE10 Developer Preview and Opera Next 12.00 alpha, it's offset by 125px. The spec just changed to make Chrome's behavior correct, to match computed values of practically all other properties: http://dvcs.w3.org/hg/csswg/rev/b491a045f29a
This is likely to be inconsistent with the requirement that transform values not be rounded until as late as possible, since computing em into pixels rounds...
Per current spec, Gecko's behavior here is completely wrong right now. Better approximately right than completely wrong. :)
I think this broke when 3-D transforms landed. (I think there might be another bug on this somewhere, too.)