Edit: Replies to this thread indicate this is not fully correct as it exists on all browsers; and is likely an ad thing.
It would not be the first time Google was caught doing this. A couple years ago they were caught breaking apps like google maps if your user agent string wasnt chrome.
But recently I've noticed they can tell regardless of that string. So my guess is that they've hidden fingerprinting code in the chrome browser
This is not correct.
Most of the posts/articles reference following reddit post: https://old.reddit.com/r/firefox/comments/17ywbjj/whenever_i_open_a_youtube_video_in_a_new_tab_its/k9w3ei4/ . It shows the code from your screenshot. However the code does not check the user agent and is not injected server side (I checked by user agent spoofing and using a freshly installed chrome). So it will run on every browser and cannot be used against some specific ones.
There is an answer to the post everyone seems to reference, which goes a bit deeper into what the code could do: https://old.reddit.com/r/firefox/comments/17ywbjj/whenever_i_open_a_youtube_video_in_a_new_tab_its/ka08uqj/
yea there does appear to be delay but it doesnt target firefox users specifically (i think) or atleast isn't obvious to me cuz the code is obfuscated. more likely related to ads (since there is a 5 second delay before you can skip ads). anti-adblock maybe yes.
Can confirm it's happening to me even on Chrome (they won't let me remove it at work
)
uBlock on firefox here, no User Agent spoofing, videos load in ~1-2 seconds as normal still. Wouldn't surprise me if it's used in nicher circumstances though.
I will make a call to a friend of mine called EU to solve this problem.