This sounds like something that would be in the back end so likely not. But if spoofing user agents fixes the problem then I'd say it's evidence enough to warrant a deeper look.
Yes. User Agent is a http header that is part of every request you send to a server. As such, it is 100% client side and it can be whatever you want, it's just a text string.
For layman users, I'd recommend using an addon for it, e.g.
https://addons.mozilla.org/en-US/firefox/addon/user-agent-string-switcher/
it's pretty inconclusive if there's no context for how that code is called. I'm kinda confused why the article wouldn't have provided any additional detail other than a single line of code. why bother digging at all?
it's part of their anti-adblock code. without going into too much details, they can instantly find out whether ad-block is trying to do anything on chrome, but on firefox they need a 5 sec delay
Which is honestly to Firefox's credit. Making it harder to find out stuff about your browser is a good thing, unless it has to do with feature support.
But the fact that they don't give a shit and are willing to ruin the user experience for it, that's despicable.
Have you read past that screenshot of the code, though? It says the problem was not limited to Firefox, it seems Edge users reported problems as well. Anecdotally, I did experience that delay problem on Thorium this weekend as well. I have seen a variation of this problem almost a month ago, where sometimes the video would take a long time (like, over a minute, sometimes) to load, or often just not load at all. So I just chalked it up to Youtube having done something stupid on their end.
not saying we should worry for them, but youtube is run at a loss so they do actually need money from SOMEWHERE to maintain youtube. youtube still sucks and this is definitely not the way to win over users but thems the facts