Except that it has been found in the past that Google/YouTube has been serving different html to Firefox than to Chrome. If they would be serving the same html, then you might have a point. But even then, Google can push through non standard changes to both chrome and YouTube before Firefox even has had a chance of making it compatible.
Chozo@fedia.io 1 week ago
For what it's worth, the bug in this article is partially replicable in Chrome, and isn't even unique to YouTube. Due to the way I keep my windows positioned, I sometimes get the mobile layout of a web page on my desktop because I opened it in a narrow window, and quite often those sites will go into the same flickering, rapid loop of layout adjustments the article describes. I ran into this quite often while I was applying for jobs last year.
Though I've not seen the extensive resource usage happening when Chrome does this. That part of it could very well be a side effect that's compounded by the user agent shenanigans Google does with YouTube.