This gives us some background, but it's still slowing down firefox with no relation to the video content.
It's radically different.
How come switching to User Agent to Chrome fixed it for that Reddit OP? Does it omit this if UA is changed?
When they first introduced anti-adblock crap, you could evade the banner by switching UAs. I'd say it's fair to assume that switching UAs triggers some other code path and this function never gets called.