When APZ is enabled (as it is for Mac on Nightly), the network monitor in DevTools has lots of checkerboarding and you can easily scroll enough that we never re-paint the request list at all. STR: 1. Visit a site with many requests such as this demo: http://bgrins.github.io/devtools-demos/misc/requests.html 2. Open the net monitor quickly to catch requests (or reload once it is open): Tools -> Web Developer -> Network 3. Once at least ~200 requests have loaded, try to scroll using the touchpad * You can check the demo page, it lists a count of loaded requests ER: The list of requests in the net monitor should scroll smoothly. AR: With a large request list, scrolling easily triggers checkerboarding. In some cases, the request list is even left unpainted (blank) forever. Scrolling again slowly repaints it back again. Disabling APZ by flipping "layers.async-pan-zoom.enabled" makes scrolling perf much better here.

I'm able to reproduce the perma-checkerboard using these STR on the latest OS X desktop nightly, although I have to scroll really aggressively to hit it. It seems like if the scroll position reaches the end of the scrollframe while it's in a temporary checkerboarding state, it doesn't do a repaint and remains perma-checkerboarded. We should definitely fix this.

No problem on Win8.1 (current win32 nightly)

Can you still reproduce this on the latest nightly? The scrolling behavior is quite bad before bug 1208554, and appears to have improved a lot after. It wouldn't fix the problem in comment #1 but it should make it much harder to checkerboard.

(In reply to David Anderson [:dvander] from comment #3) > Can you still reproduce this on the latest nightly? The scrolling behavior > is quite bad before bug 1208554, and appears to have improved a lot after. > > It wouldn't fix the problem in comment #1 but it should make it much harder > to checkerboard. I agree with your evaluation. It is much better in the general case. It's still possible to perma-checkboard if you scroll aggressively, but it does seem harder to trigger that case.

Since this is less frequent now I'm downgrading the importance of it with respect to shipping APZ.

It works for me in win 10 and mac 10.11 (OS X El Capitan).

My Test Environments: ------------------- Version 47.0a1 Build ID 20160201030241 Update Channel nightly User Agent Mozilla/5.0 (Macintosh; Intel Mac OS X 10.11; rv:47.0) Gecko/20100101 Firefox/47.0 and Version 47.0a1 Build ID 20160201030241 Update Channel nightly User Agent Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:47.0) Gecko/20100101 Firefox/47.0

I also can't hit the perma-checkerboarding any more, and in general this seems a lot better. :jryans, please reopen this if you still see it in Nightly.

I agree, it appears to be fixed. I can't hit the perma-checkerboard either. Great work, whoever fixed it! :)