I learned about this through an article - Truly a game changer and something I've been seeking. I find a book that I like, go to my library website to see if they have any copies, if not, consider purchasing which makes me go to another site. This extension automatically allows you to preview how many copies your library has of a book you're reading a review of. Truly - AMAZING. It's worth the caps. Such a time saver. Thank you!!!!