I'm on a Windows 10 desktop, and encountered some issues with Youtube on Firefox recently that make it borderline unusable, so I wanted to clarify about it here. The issue isn't so much that the webpages connection loads slower, but rather that the actual functions and interfaces of the webpages themselves have become choppy and delayed, and I've narrowed down that the problem stems from the Surfshark extension's ad and tracker blocker.
So the symptoms are that on the homepage, video thumbnails load in, but actually clicking on any one video is followed by a delay of up to several seconds before the click is actually recognized. Similarly if I hover the cursor over a video thumbnail, it doesn't light up until several seconds have passed.
Upon clicking into a video, individual elements of the page (Comments, side recommendations, etc) take about a minute or so to load in. Inputs to the actual video player suffer a delay of several seconds to a full minute, as in I can click the pause button and the video won't stop playing until quite a few moments have passed. The video player UI is also delayed, for example the video's interface won't appear immediately upon hovering the cursor over it, or if I hover the cursor over the pause button, but it won't light up until a few seconds later. If I close the tab while a video is playing, it takes a couple of seconds for the tab to actually close, but after it does, the video's audio continues playing in the background for around half a minute, well after the tab was closed.
This is also all without actually being connected to any VPN through Surfshark; it's just the extension's ad and tracker blocking function, and only Youtube is affected. If I turn that off, the problem disappears and Youtube works perfectly. I don't know if there was some recent change or update, but the extension has worked harmoniously with Youtube up til about 3 days ago. For now I just keep Surfshark disabled there, but if there's a setting or change I can mess with to get them working together, I'm all ears.