The answer was to allow websites to choose their fonts. Problem resolved. Please close this question.

Are you running the Firefox 38.3.0 ESR version or the Firefox 38 release?

• Help > About

If you are on the release update channel then please update to the current Firefox 41.0.1 release.

• Help > About Firefox

• https://support.mozilla.org/kb/update-firefox-latest-version.

Note that missing icons are usually supplied by a font that is downloaded from the server (@font-face) as you might see by little boxes that show the hex code of the characters instead. If you have a font installed that covers this Unicode range then you may see a real (CJK) character and not the little box with the CSS code.

Make sure that you allow pages to choose their own fonts.

• Tools > Options > Content : Fonts & Colors > Advanced: [X] "Allow pages to choose their own fonts, instead of my selections above"

You can check the gfx.downloadable_fonts.enabled pref on the about:config page and make sure that it is set to true (if necessary double-click the line to toggle its value to true).

Firefox 41 will allow icon fonts that use PUA code points to work with the font setting in "Options/Preferences > Content > Colors" disabled. When unsupported code points are used then you see the little boxes with the hex code.

• http://www.ghacks.net/2015/07/21/firefox-41-mozilla-modifies-how-icon-fonts-are-handled-by-the-browser/

I am running 38.2.1. I cannot update it to the latest because that's limited by work administrator. Thanks very much. I was able to get it work properly by allowing websites to choose their fonts.