If a website viewed in Firefox looks like it's all jacked up but in other browsers it's okay then you may have switched off allowing the site to download and/or display a custom font.
This is usually the case if you are seeing gibberish like a small box with numbers and letters on top of each other on parts of the website where you would expect to see custom icons.
To fix this, go to
Tools → Options → Content → Fonts & Colors → Advanced
Make sure the following has a check mark in the box:
☑ Allow characters to choose their own fonts, instead of my selections above
OK, OK, and you will now see the font icons the site has set up.