This is happening to me on Android (Chrome); the page completely freezes and can't be scrolled for 3-5 seconds. I assumed it was my phone reflowing or something, but I feel like it shouldn't be that bad, and if it's also happening on MBA, it really shouldn't be that bad

Same delay on iOS, but still much faster than scrolling past 700+ comments.

Something is wrong. I just collapsed the top thread (733 comments) and it was almost instant. I'm running Firefox 48 on OS X Mavericks on a non-retina MB Pro. NoScript is loaded but ycombinator whitelisted.

Noticeably slow on my OSX Chrome (mid-2014 MBP) as well. Is there an issue tracker where we can submit CPU profiles and whatnot?

Experiencing the same issue on Firefox on OSX.