I found a 2009 style youtube frontend, it seems to have a flash and html5 player. It might work in Windows 9x but what about the experience?

http://yt2009.giabs.ovh/

I tried it briefly. The player doesn't work in RT's Retrozilla or KM 1.5.4 TLS1.2 and it works in RT's Firefox 3.6 (KernelEx needed) only for some seconds here. It seems to run well in Firefox 9.0.1 (KernelEx needed).

Do you have Flash Player enabled? I think it is required. In theory, Firefox 3.x and newer has html5 video support, so maybe it uses the html5 player. But as far as I read, the player also has a flash version.

Yes, the flash player is enabled in the old browsers. My installed version is 21.0.0.242. I also tried the frontend in Opera 10 without success. The player also doesn't work in Opera here.

Thank you. I tried it. In Firefox 9, the CPU usage is 15-25%. In Opera 12.02, only 7-8%, after the video is fully loaded. Sometimes it takes a few seconds to load or doesn't fully load. In both cases, only HTML5 seems to be used. Switching to HD doesn't work. Opera also requires disguising itself as Firefox or opening the same page in Firefox in parallel (I can't imagine how this can be related, but there is a fact). It's not very stable. In Mypal 29, it works noticeably better and even switches to HD (But not everyone in this browser has sound, so it's less relevant). All that's missing is a button for explicitly switching to FlashPlayer, as well as adjusting the playback speed and quality selection. Otherwise good.