Nice, hadn't seen those sliders before. Must be a new feature.

It's been around for some time. Not sure how long, but I don't remember it ever not being there.

I still don't see those sliders. Is it something you have to enable in the preferences? Is it mobile-only or something (I don't use a browser on my phone at all, so I wouldn't know...)

I see them now with Firefox on desktop, didn't enable anything specific. They definitely weren't there when I last used the blocking feature, which was probably some time last year.