<!DOCTYPE html> <html class="reftest-wait"> <head> <title>mfrac linethickness</title> <script type="text/javascript"> function doTest() { document.getElementById("testMfrac").removeAttribute("linethickness"); document.documentElement.removeAttribute("class"); } window.addEventListener("MozReftestInvalidate",doTest); </script> </head> <body> <math> <mfrac id="testMfrac" style="font-size: 300%" linethickness="50%"> <mi>a</mi> <mi>b</mi> </mfrac> </math> </body> </html>