Unpaywall does now indeed work on both Firefox and Chrome. Kudos to you.

Bonus points for "for the Open Access nerds: the Unpaywall tab can change colors to indicate Green or Gold OA, too. Enable it in settings."

This add-on has helped me find a lot of research papers I needed for my thesis. Please keep up the good work. I am amazed it has been this useful in so little time but I found a solid 90% of the research papers I needed!