Try installing the MathML fonts (e.g. STIX). They are available on the Mozilla page: https://developer.mozilla.org/en-US/docs/Mozilla/MathML_Project/Fonts For the invisible operators, you'll still see bug 115786, though.

The STIX fonts are installed, using the MathML Font Installer from the Mozilla site (https://developer.mozilla.org/@api/deki/files/6388/=MathML-fonts.msi). I also tried installing them manually, but this made no difference. Interestingly, this Mozilla test page (https://developer.mozilla.org/en-US/docs/Mozilla/MathML_Project/Fonts/Test?redirectlocale=en-US&redirectslug=Mozilla_MathML_Project%2FFonts%2FTest) does not display properly on Mac or Windows, although the "MathML Torture Test" (https://developer.mozilla.org/en-US/docs/Mozilla/MathML_Project/MathML_Torture_Test?redirectlocale=en-US&redirectslug=Mozilla_MathML_Project%2FMathML_Torture_Test) seems to work properly on Mac and partially on Windows. After running the MathML Fonts installer, I no longer see an "X inside a box" glyph for the invisible times. However, the greek characters up port for the "multi scripts & greek alphabet" test on https://eyeasme.com/Joe/MathML/MathML_browser_test.html no longer renders at all (showing just 5 empty box glyphs instead of the circle of greek characters surrounding a capital Pi character. Inspecting the elements in the WebInspector shows that the mathml.css styles are being applied, and that WebKit recognizes that it should be using MathJax_Main or STIXGeneral fonts for rendering.

(In reply to comment #2) > Interestingly, this Mozilla test page (https://developer.mozilla.org/en-US/docs/Mozilla/MathML_Project/Fonts/Test?redirectlocale=en-US&redirectslug=Mozilla_MathML_Project%2FFonts%2FTest) does not display properly on Mac or Windows, To draw the grid, this test page uses vertical stretchy U+221A SQUARE ROOT and horizontal stretchy U+23DC TOP PARENTHESIS, the minsize attribute and operator stretching in <mover>. I think only the last feature is supported by WebKit at the moment, so I'm not surprise it does not work. See the related bug 119038 and bug 72828. > After running the MathML Fonts installer, I no longer see an "X inside a box" glyph for the invisible times. However, the greek characters up port for the "multi scripts & greek alphabet" test on https://eyeasme.com/Joe/MathML/MathML_browser_test.html no longer renders at all (showing just 5 empty box glyphs instead of the circle of greek characters surrounding a capital Pi character. Could you try to check with HTML-only content like <span>&pi;</span>, <span style="font-family: STIXGeneral">&pi;</span>, <span style="font-family: italic;">&pi;</span> etc That might well be a font/text issue unrelated to MathML.

(In reply to comment #3) > To draw the grid, this test page uses vertical stretchy U+221A SQUARE ROOT and horizontal stretchy U+23DC TOP PARENTHESIS, the minsize attribute and operator stretching in <mover>. I think only the last feature is supported by WebKit at the moment Well, actually horizontal stretching is not supported at all.

(In reply to comment #2) > After running the MathML Fonts installer, I no longer see an "X inside a box" glyph for the invisible times. However, the greek characters up port for the "multi scripts & greek alphabet" test on https://eyeasme.com/Joe/MathML/MathML_browser_test.html no longer renders at all (showing just 5 empty box glyphs instead of the circle of greek characters surrounding a capital Pi character. OK, I just checked the page and I'm guessing you are talking about the fraktur letters, not the greek ones. The fraktur characters are in Unicode Plane 1, so I suspect it is the old bug 24230.

(In reply to comment #3) > (In reply to comment #2) > Could you try to check with HTML-only content like <span>&pi;</span>, <span style="font-family: STIXGeneral">&pi;</span>, <span style="font-family: italic;">&pi;</span> etc That might well be a font/text issue unrelated to MathML. You are absolutely right; these glyphs display properly.

(In reply to comment #5) > (In reply to comment #2) > OK, I just checked the page and I'm guessing you are talking about the fraktur letters, not the greek ones. The fraktur characters are in Unicode Plane 1, so I suspect it is the old bug 24230. Indeed. My ignorance has been revealed! The fraktur letters were the issue I was trying to describe. Conclusion: 1. My original problem was due to missing fonts. We should probably update DRT/WInLauncher or perhaps update-webkit to check for the presence of these fonts when the MATHML feature is turned on. 2. The second issue I noticed with the fraktur letters is a duplicate of Bug 24230. Closing as a duplicate, and opening a new bug for the test configuration checks. *** This bug has been marked as a duplicate of bug 24230 ***

See Bug 122568 for checks to ensure MathML is installed.