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.

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

• Firefox > Preferences > 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).

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

cd1515 said

images don't fully load in firefox only, see attached screenshot, empty white boxes top right, between "stream options" and "upgrade"

That fixed it, thanks!