<mlabeledtr> is used in the code generated by MathJax from LaTeX (for equation labeling) but browsers like Webkit, Gecko or Opera do not support this element: https://bugzilla.mozilla.org/show_bug.cgi?id=689641 https://bugs.webkit.org/show_bug.cgi?id=85732 http://www.w3.org/TR/mathml-for-css/#d2e2181 cf the discussion on mathjax-dev