Safari seems to be able to do a much more smooth job at scrolling https://verily.com/ than we can.
Could you verify that the page is async-scrolling, for example by enabling paint flashing (nglayout.debug.paint_flashing) and verifying that the page isn't repainted on every scroll? If so, a profile would be helpful to understand the slowdown. For me, testing on Linux, the page is async-scrolling, and my perception of the scrolling smoothness is fine (but I don't have Safari nearby to compare it to).
With paintflashing I see the background of the page (and many other parts) continuously repainting all the time, even if I'm not scrolling. OS X aurora build from March 17.
status-firefox48: --- → affected
Version: unspecified → 48 Branch
It's probably eating CPU unnecessarily as well.
Actually I'll file a new bug for the infinite painting, and mark this dependent on that. There might be more going on here, best to keep the issues separate.
Depends on: 1260799
The infinite painting, combined with slow texture upload, are what's causing the stuttery scrolling. Texture upload happens on the compositor thread and blocks composition.
Trying to make sure all jank buga have "jank" in the summary.
Summary: Scrolling on verily.com is stuttery → Scrolling on verily.com is stuttery/janky
status-firefox48: affected → wontfix
status-firefox49: --- → affected
status-firefox50: --- → affected
Depends on: 1261166
OS: Unspecified → Mac OS X
Priority: -- → P3
Depends on: 1282797
status-firefox49: affected → wontfix
status-firefox50: affected → fix-optional
status-firefox51: --- → affected
status-firefox50: fix-optional → wontfix
status-firefox51: affected → wontfix
status-firefox52: --- → wontfix
status-firefox53: --- → affected
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