I noticed this myself as I had been using Firefox with ublock to mostly listen to music on youtube.
It seems like there's a sometimes-auto-downgrading where any video above 360 p gets throttled and causes buffering. I've recently been trying out a Chrome extension called Clear Skies which has been working well. It's not an adblocker but it does hide and skip ads and avoids the performance hit that I was seeing previously when viewing youtube with Firefox.
It seems like there's a sometimes-auto-downgrading where any video above 360 p gets throttled and causes buffering. I've recently been trying out a Chrome extension called Clear Skies which has been working well. It's not an adblocker but it does hide and skip ads and avoids the performance hit that I was seeing previously when viewing youtube with Firefox.