Desktop toolkits expose list/scroll virtualization to apps natively and expect you to use it, so they aren't optimized for the case of a giant single vertical l

Desktop toolkits expose list/scroll virtualization to apps natively and expect you to use it, so they aren't optimized for the case of a giant single vertical layout. HTML doesn't so devs are forced to just throw piles of markup at the browser which has to digest it all. But, that's a very web-specific UI design idiom that you just don't find in typical native apps. If you change your test to use desktop UI as it's intended to be used, and then stick say a few tens of millions of buttons in it, then the browser will find it much harder and the desktop toolkit won't break a sweat.