The layout test LayoutTests/fast/block/float/009.html fails in the case when the width of a div is given in em. In this case, the width is calculated using defaultFontSize. This variable is set up first in qwebsettings.cpp to 14, then in DumprenderTree.cpp to 13. That's why 10em results in 130px instead of 140px. If we set back the value of defaultFontSize in DRT from 13 to 14, the test succeeds. Alternally, we could have a qt-specific result for this test. Also I have to mention that it's related to the missing proper implementation of unitsPerEm() in the qt font.
Maybe it would be good to fix this in Qt before the 4.6 release? Do you think it should be hard to fix?
Committed r46974: <http://trac.webkit.org/changeset/46974>