FirstComment allows you to find the earliest (up to first 20) comments on a given video.
YouTube API is used to fetch the comments, so before you start using the service, make sure to paste your API key in "FirstComment.js" file. Click here for more information on how to obtain the key.
Note: due to the limited number of API requests you are allowed to make per day, trying to fetch the first comments on bigger, multimillion views videos is likely not going to give correct results. If you'd like to fetch those, you would have to ask Google to up your daily API limit.