What sites are these? Fonts if they aren't compatible with the Browser won't load. That also becomes a security issue if fonts can embedd their own custom software into the Browser without verify they are safe.

I didn't mean that. Just an exception for existing feature. You didn't understand the question.

There exists option to enable or disable custom fonts from websites. Now, I thought there must be an option to add sites to exception but there isn't it seems.

For example if I have used custom font and turned 'let websites use their fonts' off, I can't add any individual site to exception so it can load it's fonts but not everyone.

Why do you want to disable website fonts in Firefox ?

These days a lot of websites use special icon fonts that are downloaded from internet. When you block remote fonts then you won't see such icons (you may see a little box with the hex code) and otherwise websites might be affected if you disable website fonts. Blocking or allowing remote fonts on specific websites is easier by using a content blocking extension like uBlock Origin.

• https://addons.mozilla.org/firefox/addon/ublock-origin/

Again! You are missing the whole point.

I have no issues with that, I'm on Windows, I'm using Apple fonts and forcing using Firefox on every other website that's why I'm not allowing them to use their fonts using FIREFOX'S OWN FONT SETTING that allows users to disable custom fonts on sites.