yes. I block iframes globally and the web never been better.
it will show a checkered pattern with a link to open the frame in another window. so you don't even have to whitelist sites or anything. if you care about the frame, like for a embedded video, just open it on its own tab with a single click
uMatrix can block frames and js requests on a domain/sub-domain level. afaik, it can't block at url level, if that's what you meant.
That said, uMatrix, from what I remember, uses the webRequest api which does work from urls. So if you know JS, you can always create an extension and add your own filter.
To be clear, on the JS side I'm talking about providing whitelist-only access to things like the ambient light level, which is provided through a standardized browser API.
