User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Firefox/68.0

Steps to reproduce:

Visit https://givingtools.com/ask and scroll all the way to the bottom of the page. Then scroll back up to the top and click the "Q&A" navigation link. Scroll down a little bit and you'll see content from the previous page still being rendered behind the expandable questions.

I've tested this on the latest Firefox Nightly (v68.0a1 (2019-05-02) (64-bit)) as well as on my laptop running v66.03. Both running Ubuntu 18.04. My boss originally discovered this issue on his Mac running Firefox v66.0.1.

Actual results:

Content that has been removed is still visible until something overlays it (e.g. inspect element box overlays, resizing the page, switching tabs).

Expected results:

Well, I don't expect this glitch to appear.

I can also reproduce the issue on Nightly68.0a1 Windows10.

esr60 is also affected :(

Regression window:
https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=fa3be8644d73a8ef20333924c11b70c5bc034fdf&tochange=ce7f71c2f402beaebf1485323144830e8743fffa

Regressed by: Bug 1382534

And I can confirm that set layers.async-pan-zoom.enabled to false fixes the issue on Nightly68.0a1 Windows10.

I can also confirm that setting layers.async-pan-zoom.enabled to false and restarting Firefox also fixes the issue for me on Nightly 68.0a1 Ubuntu 18.04.

What method are you using to perform the scroll (keyboard, mousewheel, touchpad, autoscroll, etc.)?

(In reply to Botond Ballo [:botond] from comment #6)

What method are you using to perform the scroll (keyboard, mousewheel, touchpad, autoscroll, etc.)?

I'm using the mouse wheel, but I can also reproduce it if I drag the scroll bar.

I can't reproduce it, however, if I use the page up/down keys or up/down arrow keys.

At least I can reproduce the issue with following method
using mouse wheel
using autoscroll
using dragging thumb of scrollbar.

I cannot reproduce the issue using keyboard(I tried several times, but not reproduced).
I do not have touchpad device.

I have not been able to reproduce this so far, testing the latest Nightly on Debian stable. I've tried all three of the mentioned methods.

I can reproduce this on macOS. WebRender is off.

Based on the symptoms, this seems like a latent graphics bug that was exposed by layerizing masks, rather than a bug in the mask clip computation (which is what previous regressions from bug 1382534 have been).

Build ID 20190506130308
User Agent Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:68.0) Gecko/20100101 Firefox/68.0

screencast https://youtu.be/yO2z6VnuyuU

I'm not seeing this issue anymore, probably because we are now lazy loading those images (as of 5/20/19).

I can still reproduce the issue on Nightly69.0a1 Windows10.
Build ID 20190604214415
User Agent Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:69.0) Gecko/20100101 Firefox/69.0