Youtube streams from googlevideo.com and Facebook from fbcdn.net. You would need to add both of them to the adblocker.
Sorry I'm so late responding, have been laid low with a superbug!
Those URLs are so helpful, thank you, what a difference! I wonder if you have one for Twitter also?
(Hope I don't keep bothering you with new ones, but I think those 3 are the main culprits.)
You can see the source url of any stream you have captured by selecting it and then Menu > Properties or press Alt+Enter to display the Properties window.
The adblocker just requires the domain part of the url.
In particular, I need to prevent any downloads whatsoever from YouTube and Facebook, while I continue to monitor the streams I am interested in.
I have to auto-refresh browsers to allow for dropouts of streams to be re-picked up, plus I check notifications from YT and FB and watch videos on those sites - but I NEVER want them downloaded.
I added YT.com and FB.com to the block-ads setting but it hasn't helped.