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.

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

it was installed by default, but it does not help. I don't have part of the picture. the problem is in another place

Do you still see the little boxes with the hex code?

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).

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

You can open the Web Console (Firefox/Tools > Web Developer).

• https://developer.mozilla.org/Tools/Web_Console

Check if there are error message with regard to downloading fonts. You can also check the Network tab for files with file size zero.

You can reload web page(s) and bypass the cache to refresh possibly outdated or corrupted files.

• Hold down the Shift key and left-click the Reload button
• Press "Ctrl + F5" or press "Ctrl + Shift + R" (Windows,Linux)
• Press "Command + Shift + R" (Mac)