Apparently, the Youtube API documented here - https://developers.google.com/youtube/v3/docs/videos https://developers.google.com/youtube/v3/docs/videos - return

Apparently, the Youtube API documented here - https://developers.google.com/youtube/v3/docs/videos https://developers.google.com/youtube/v3/docs/videos - returns both likes and dislikes. All Google did was remove the rendering of that API response field onto the webpage. Extensions probably acquire the video url and make their own API call just to retrieve the dislike count. To me, that seems cleaner than trying to snoop on the main API call response (I think extensions might not have access to those, maybe they do). Basically, the data is available via API calls.