Interesting. I was looking at the Typekit page: https://typekit.com/fonts/source-sans-pro https://typekit.com/fonts/source-sans-pro On the specimens there, So

Interesting. I was looking at the Typekit page: https://typekit.com/fonts/source-sans-pro https://typekit.com/fonts/source-sans-pro On the specimens there, Source Sans looks terrible at almost any sensible body text size in Firefox on Windows XP. However, I was comparing those results with samples of Open Sans from Google Web Fonts, which look much better. Apologies if this wasn’t a fair comparison.