Hi David
Thanks for getting back to me so fast.
Just marking some text in a blog post bold using the normal editor. However, I did a bit more digging and it seems to be a Firefox issue.
Even looking at your Demo of “Article” it looks like different font weight in Firefox vs Chrome and Edge.
Removing the font variants (See link below) will fix the problem and make the site appear almost identical across browsers (Although not entirely. Heading are still a bit different)
https://docs.generatepress.com/article/google-font-variants/
Removing the font variants is not ideal, but not the end of the world either 🙂