User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:65.0) Gecko/20100101 Firefox/65.0 Steps to reproduce: enable WR Go to https://kangax.github.io/compat-table/esnext/ Scroll till the red table occupies most of the screen put mouse inside the table, and then try to scroll with the mouse wheel Actual results: there is latency while scrolling. Something like when you scroll, it starts slowly, but also ends slowly and scrolls more than what you want to scroll Profile shows large jank in the parent process, waiting for APZC Expected results: not so. non-WR is very smooth non-WR: https://perfht.ml/2L4rX6W (despite what the profile may say, scrolling was always very smooth) WR: https://perfht.ml/2L67b6M

I scrolled just a tiny bit. But the total amount scrolled was larger than expected, and the scrolling didnt stop when I stopped scrolling.

here is a more extreme version : https://perfht.ml/2L3PkgR could be a dupe of bug 1480964/bug 1497090/bug 1494163 .