STR: 1. Scroll down https://medium.com/@treystout/engineering-principles-c58f5f8c264b Expected: Regular scrolling. Actual: Flickering, vertically scaled parts of the Firefox UI appearing in the page content.

FWIW, I don't see this on my win8.1 machine. Mac issue?

I see a noticeable checker-boarding when scrolling this page very quickly but otherwise it's fine.

I see this in both e10s and non-e10s windows on OS X 10.9.5 in a nightly build.

Note that I find this easiest to reproduce when scrolling slowly from the top of the page. Past a certain point the problem will no longer reproduce, and any attempt to return to the top and try again will not demonstrate the problem.

I can't seem to reproduce this as well. Does this only happen for you on nightly? Is this happening on Developer Edition / Release?

I cannot reproduce any problems locally. Josh, could you investigate if this is a regression and if so use mozregression to narrow it down?

I cannot reproduce in a developer edition build.

Interestingly I can't reproduce in a new profile, either.

(In reply to Josh Matthews [:jdm] from comment #8) > Interestingly I can't reproduce in a new profile, either. Maybe an add-on you installed, a pref you changed, or something in your session is causing this?

It might be a combination of APZ and an add-on. Can you try setting layers.async-pan-zoom.enabled to false, restarting the browser and seeing if it still happens? If it doesn't, can you bisect through your addons to see if one of them is a factor?

With APZ disabled I cannot reproduce the problem.

I discovered that the glitch only appears when the page is in a non-default zoom level.

Also I got https://crash-stats.mozilla.com/report/index/0a6b5259-107d-499f-a8d4-c91a62151118 when closing the instance of Nightly that was demonstrating the glitch.

I tried reproducing on my non-Retina air and couldn't. I think in order to repro this you need: 1) APZ enabled 2) A retina display, with the Firefox window taking up most/all of the screen 3) Full zoom applied

Thanks Josh, I can now reproduce this on my MacBook Pro (Retina, 13-inch, Late 2013) with the added factor of this requiring a non-default zoom level.

I'm pretty sure that bug 1021845 will fix this.

APZ Product Triage: P1.

Josh or Anthony, could you check to see if the problem is fixed in the latest nightly (which includes the fix for bug 1021845)?

(In reply to Botond Ballo [:botond] from comment #19) > Josh or Anthony, could you check to see if the problem is fixed in the > latest nightly (which includes the fix for bug 1021845)? I cannot reproduce this with today's Nightly build.