Hi This can happen if you block remote fonts that are downloaded from internet or otherwise block downloadable fonts.

Make sure you allow pages to choose their own fonts.

• Settings -> General: Fonts & Colors -> Advanced
  [X] "Allow pages to choose their own fonts, instead of your selections above"

If you use uBlock Origin make sure not to "block remote fonts".

I don't see "Fonts &Colors" I am using a Macbook pro.

You can look under:

• Settings -> General -> Language and Appearance -> Fonts -> Advanced

Thanks, that worked. I was looking at the wrong header. On my computer at the top under "Firefox" it says "Preferences" instead of "Settings"

Frederick