Through its "Fonts" dialog, Firefox allows users to select the fonts to be used by pages, and then there is the option to "Allow pages to choose their own fonts, instead of your selections above". If such option is not selected, then pages can't choose any font of their own, and this behavior breaks the rendition of pages that use fonts like Font Awesome for graphical effects, not text. Therefore, when "Allow pages to choose their own fonts, instead of your selections above" is not selected, Firefox should let users specify exceptions for some fonts (Font Awesome could be an initial default item).
Thank you.