Generate large YouTube video thumbnails when posting on Facebook: YouTube-xl.com
Browser extension (Chrome and Firefox) allows you to generate large thumbnails for links to YouTube videos instead of the small ones Facebook normally creates.
It works only by either going to the home page of this service and inserting the URL of a YT video or by installing the Chrome extension and going over to the YouTube video page where is located the clip you want to post on Facebook.
100% free.
My comment: Valid alternative to YT2FB.com. Does what it promises reliably.
*The result is essentially the same, though the quality of the thumbnail generated is slightly different. YT2FB offers (at a price) a Pro Toolbox which allows you also to further personalize the title and description of the post. Another advantage of YT2FB is that it allows to create a link for a YT video, without having to go to its page.
Try it out now: https://www.youtube-xl.com/
Chrome extension: https://chrome.google.com/webstore/detail/yt-xl/amanljhhcdjglabdfekbkhehoocpohlp
Firefox add-on: https://addons.mozilla.org/en-US/firefox/addon/yt-xl/