Our MathML support uses exclusively the [https://bugzilla.mozilla.org/show_bug.cgi?id=569195 STIX fonts] to stretch mathematical symbols. The purpose of this project is to prepare support for various other unicode fonts such that [https://bugzilla.mozilla.org/show_bug.cgi?id=407439 Asana Math], [https://bugzilla.mozilla.org/show_bug.cgi?id=372351 Cambria Math] or [https://bugzilla.mozilla.org/show_bug.cgi?id=622576 Neo Euler].
The first step is to move nsMathMLChar from using nsIRenderingContext to gfxFontGroup. After that, the key feature to implement will be an interface to read [https://bugzilla.mozilla.org/show_bug.cgi?id=407059 OpenType MATH table].