Short answer: If any stylesheet is unavailable because of CORS, then fall back to setting font-family on every element on the page
Longer Explanation: Many sites load their stylesheets from sub-domains or other sites. Those are unavailable to scripts because of Cross-site Origin security. Since this extension cant then modify the stylesheet, it takes the longer route of modifying each element on the page that can contain text to specify the sans-serif font family.

Added option to log the names of fonts removed to the browser's console log panel, in settings.
Bug fix where some fonts not removed.

Add an Option page where you can specify which fonts are allowed.
Unfortunately one has to inspect the page with this extension disabled in order to see what font is being used. Contact the developer if you don't know how to do that.

Added Font Awesome to the allowed font list.

Allow font with "glyph" in their names as well.