diff --git a/gfx/thebes/gfxFontPrefLangList.h b/gfx/thebes/gfxFontPrefLangList.h
index bc121884d27..804b2b17efc 100644
--- a/gfx/thebes/gfxFontPrefLangList.h
+++ b/gfx/thebes/gfxFontPrefLangList.h
@@ -27,6 +27,7 @@ FONT_PREF_LANG(Gujarati, "x-gujr", x_gujr),
 FONT_PREF_LANG(Gurmukhi, "x-guru", x_guru),
 FONT_PREF_LANG(Khmer, "x-khmr", x_khmr),
 FONT_PREF_LANG(Malayalam, "x-mlym", x_mlym),
+FONT_PREF_LANG(Mathematics, "x-math", x_math),
 FONT_PREF_LANG(Oriya, "x-orya", x_orya),
 FONT_PREF_LANG(Telugu, "x-telu", x_telu),
 FONT_PREF_LANG(Kannada, "x-knda", x_knda),
diff --git a/modules/libpref/init/all.js b/modules/libpref/init/all.js
index e2264f21d12..c179146f22d 100644
--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -2715,7 +2715,10 @@ pref("font.size.fixed.zh-TW", 16);
 
 // mathml.css sets font-size to "inherit" and font-family to "serif" so only
 // font.name.*.x-math and font.minimum-size.x-math are really relevant.
+pref("font.default.x-math", "serif");
 pref("font.minimum-size.x-math", 0);
+pref("font.size.variable.x-math", 16);
+pref("font.size.fixed.x-math", 13);
 
 /*
  * A value greater than zero enables font size inflation for