Technology

Not trying to defend Chrome here as I dislike their other behaviours, but just from what's presented in the video, an alternative explanation would be caching. That is, when the reloading is triggered by the switch of user-agent, the cache is reused and thus a shorter load time.

To exclude this effect, the user needs to either

1. Spoof the user-agent and at the same time clear cache (you can disable cache when reloading through the developer's tool), or
2. Clear cache, spoof the user-agent to Chrome. Load page, disable the spoofing, reload.

I can confirm this. I signed up for the free trial of YT Premium (which I immediately cancelled, but I'll take the three months) but YT seems to be detecting that I'm on Firefox and have Ublock installed, so I'm getting the occasional 5 second forced delay, even though I'm a premium user. (They may not count the trial as being a "true" premium user, I'd suspect.)

I'm not seeing this issue on Firefox?

Here is a link of someone finding a Timeoutset: https://old.reddit.com/r/firefox/comments/17ywbjj/whenever_i_open_a_youtube_video_in_a_new_tab_its/k9w3ei4/