Created attachment 8669308 [details] Screenshot from 2015-10-03 12-09-04.png On Wikipedia and MDN, MathML takes up way too much vertical space, and matrices are similarly over-spaced. This has been going on for a little while. On my machine, the Inspector shows: line-height > 93px math > normal mathml.css:16 at https://developer.mozilla.org/en-US/docs/Mozilla/MathML_Project/MathML_Torture_Test and line-height: 71px; body > 1.5 mdn-min.css:1; math > normal mathml.css:16; at https://developer.mozilla.org/en-US/docs/Web/SVG/Attribute/transform#Types_of_transform_definition.
This is probably a duplicate of bug 1208776. STIX Math as well as some old OpenType MATH fonts do not set the USE_TYPO_METRICS flag, so they no longer work after bug 1170782. You must to upgrade your OpenType MATH to the latest version.
Thanks Frédéric; upgrading the font does fix the problem. Marking duplicate.