r240250 broke scrolling on pages using the smoothscroll.js library:
Need to see if these sites are also broken in Chrome, and if not, why not.
(In reply to Simon Fraser (smfr) from comment #2)
> Need to see if these sites are also broken in Chrome, and if not, why not.
This is the Chromium bug for sites with smoothscroll.js being broken by the change to document.documentElement as the viewport scroller: https://bugs.chromium.org/p/chromium/issues/detail?id=501568
It was fixed by this intervention in Blink, that targets smoothscroll.js:
*** This bug has been marked as a duplicate of bug 207040 ***