In addition to the fact that I remember this happening several years ago, I'm pretty sure this has been an issue for a while. When I decided to exclusively use Firefox about a year ago, YouTube as a whole would load slowly and it still does.

And I hate the fact that Google knows that they will benefit from this because, unfortunately, a majority of YouTube users are sheeple.

I started noticing how sometimes youtube just seemingly refused to load fully on my phone. I thought it was just my crap internet. But since I use Iceraven, a fork of firefox, it seems that may be why.

Does changing the user agent fix this? Anyone tried? I keep forgetting to try it myself.

Does not happen for me Safari or Firefox.

I'm not seeing any delays, 5 second or otherwise, when using Firefox.

Any extensions you'd recommend for having Firefox spoof chrome?

Once upon a time, Google wanted to kill the user-agent.

The YouTube viewing experience on FF is terrible. I have premium no ads and still manage to break the interface occasionally by clicking a new video or seeking the video playing.

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.)

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.