I use NoScript for Firefox, which can block fonts for untrusted sites. There is also a setting, in the browser itself, to universally prevent sites from from us

I use NoScript for Firefox, which can block fonts for untrusted sites. There is also a setting, in the browser itself, to universally prevent sites from from using their own font specification, so your font choices are the only ones used everywhere. I used to use that, but some sites use icon fonts (e.g. Github), so I prefer being able to whitelist specific sites with NoScript. I also set a minimum font size to maintain comfortable reading across all sites.