Oh yes, more and more sites seem to be replacing icon images with custom fonts, which usually are sp

Oh yes, more and more sites seem to be replacing icon images with custom fonts, which usually are specified with a URL for Firefox to download rather than referring to a font you might have on your system.

Currently, Firefox only has the one "all or nothing" setting for fonts: either use your preferred fonts for everything in the page, or use the page's preferred fonts. There is not currently any distinction among different kinds of fonts or different characters in the font set.

The developers have been considering options and you can read the discussion on the bug tracking site here: Bug 789788 – Not allowing pages to choose their own fonts breaks with icon fonts.

On the bug tracking site, it's generally not helpful to add comments to bugs unless there has been a request for more information from users, but you can register on the Bugzilla site and "vote" for the bug to be fixed. See:

Bugzilla Etiquette

Voting

(Note: commenting or voting may lead to getting copies of all future comments emailed to you. Depending on the nature of the comments, this may be welcome or unwelcome...)