Type about:preferences#content<enter> in the address bar. Across from fonts and colors, press the Advanced button. On the bottom, turn on Allow Web Sites To Choose Their Own.

You can check for corrupted and duplicate fonts and other font issues: http://www.thexlab.com/faqs/multipleappsquit.html - Font Book 2.0 Help: Checking for damaged fonts http://www.creativetechs.com/iq/garbled_fonts_troubleshooting_guide.html

Hello,

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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).

You can open the about:config page via the location/address bar. You can accept the warning and click "I'll be careful" to continue.

• http://kb.mozillazine.org/about:config

This will change in Firefox 41:

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