<!DOCTYPE html> <html class="reftest-wait"> <head> <title>mfrac linethickness</title> <script type="text/javascript"> function doTest() { document.getElementById("testMfrac").setAttribute("linethickness","thick"); document.documentElement.removeAttribute("class"); } window.addEventListener("MozReftestInvalidate",doTest, false); </script> </head> <body> <math> <mfrac id="testMfrac" style="font-size: 300%" linethickness="thin"> <mi> a </mi> <mi> b </mi> </mfrac> </math> </body> </html>