Agreed. I often have several tabs & windows open. I really hate the vids that start playing again on their own after I go away...
I think Google is supposed to do exactly that in an update to Chrome sometime in the fairly near future. Both them and Firefox have been gradually blocking more autoplay content but they still let quite a bit of "legitimate" sites (like YouTube and I think news websites) get away with autoplay. I think Google announced Chrome would block all autoplay (but a toggle can probably override it, like for instance for YouTube) content in the future.
I'm not sure if its any of my addons or what, but I haven't been having that specific thing happen lately (it used to on news and stuff like CNet and Yahoo where they do that popup video player if you scroll down past the video and it'd start playing again). I think Yahoo actually pauses whatever video if you scroll past it now (sometimes they'll have an article with a bunch of videos embedded in it like from NFL Network, and it'll autoplay when you scroll down and the video becomes the focal point but then will pause if you scroll past it).
I agree the default should not be autoplay (and I don't even mind when Netflix overrides me having turned it on to go "hey are you still watching?" although I think they only do that after like hours these days; Hulu used to as well but now I think they just let the toggle do its thing but the default is autoplay), but I don't think there should be legislation mandating it.
I too wish that all sites with video content gave you control over the quality settings (i.e. resolution and other), as well as having other options (I really wish YouTube would have one for streaming just the audio as there's lots of podcasts and music and other stuff where its wasting lots of bandwidth streaming a static picture like a billion times for the length of the content; I wish we could independently adjust the audio setting so we could set it to be high but the video resolution lower since I'd prioritize audio quality for a good amount of content on there). But again, I don't think it should be legislated.