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.
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.