In the current implementation, Gecko can only stretch characters in vertical/horizontal directions. Some symbols - at least diagonal arrows - should be stretchable in "diagonal" directions. Note that the MathML spec does not distinguish these directions from "vertical+horizontal", so we should add them in our private dictionary. Here is the idea: - extend the work of bug 524275 to add new directions "updiagonal", "downdiagonal" in the dictionary. - extend the work of bug 414277 to be able to use a rotation as a transform. To draw the diagonal arrows, we draw horizontal arrows with the length of the diagonal (stretched with the "parts of glyph" techniques + possibly a scale transform) and rotate using the slope of the expected diagonal as angle.