The new border rendering code uses OPERATOR_ADD to handle seams; quartz seems to have rounding issues in this that give a 1px or 2px difference from the expected result. (To reproduce: fill a square by filling two triangles the same solid color with operator add; the seam should be the solid color at the end, whereas on quartz it's not quite there.) This affects a bunch of reftests that check for drawing two or three borders at once in a solid color and expect them to match up to a div with a solid background color (e.g. a bunch of the border-* tests in pixel-rounding).
This affects fewer reftests now that bug 464970 has landed, but the underlying bug is still present.
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