Currently, this can be done with CSS in author's web page or user's custom stylesheet etc I'm not even sure a built-in mechanism exists for text fonts but maybe we want that for math fonts. See http://trac.webkit.org/wiki/MathML/Fonts#CustomizingMathFont Note that font-family in Gecko is reset to serif and the actual selection of the default math font and fallback are listed in font.name.serif.x-math and font.name-list.serif.x-math configuration options. These options are accessible from the font preference menu of Firefox. https://dxr.mozilla.org/mozilla-central/source/modules/libpref/init/all.js See also https://addons.mozilla.org/en-US/firefox/addon/mathml-font-settings/ for an example of add-on allowing font customization.
(In reply to comment #0) > Currently, this can be done with CSS in author's web page or user's custom > stylesheet etc Exactly. We don’t need a new mechanism for this unless we have some idea about how to do it better.