I swear there was an option for this previously, but now the videos play automatically whenever you visit a store page and there's no apparent option anywhere I can find it to stop the videos from automatically playing. Videos are unhelpful, sometimes rather loud, and a waste of bandwidth to those for whom that matters. Studies have shown players prefer the screenshots to the videos anyway, so you're only hurting Steam trying to shove video trailers down people's throats. The vast majority of trailers show people nothing they actually want to know about the game, and the video just distracts from actually being able to read the real information or look at screenshots that maybe show the UI so people can figure out how the game actually plays.

(Also, I just want to throw on that I hate that the screenshot popup now requires you click the little arrows that show up on the image, and there aren't useful little buttons on the bottom of the screenshot window anymore...)