I was not 100% sure where to ask this and could not find anything directly in the release notes. I have a site that simply plays an mp4 video in a html5 video element. The video is in s3 and served via cloudfront. Generally when the video is requested by the browser (chrome, ie, edge, safari, firefox <57), cloudfront pulls the entire video and caches it, then once it has the entire video it sends to the browser, then the browser gets enough (or all of it) and plays is back. For a long video (think 1GB or larger in size) this can take 20-30 seconds to begin play back. Well, v57 of firefox blows this away and responds more like HLS or MPEG-DASH playback in that it seems to pull the first few chunks and starts right away (under 2 seconds) and begin playing. I can also jump towards the end and it starts to play right away. There is no way the browser has the entire MP4 but appears to be pulling it with a WebRTC datachannel or something similar and putting it back together. I was just curious how they were doing this as it is amazing.