This looks like a recent regression.

It looks like this bad content aligns with picture caching tiles.

confirmed seeing this on my personal macbook pro as well.

I suspect this might be because I have gfx.webrender.compositor set to true.

and the regression may have been cause by bug 1604383

I saw something similar on Windows yesterday with compositor enabled. Probably best to disable compositor for now, until I have time to see what caused this. Since it happens on both compositor platforms, it's probably a bug in the WR code of the regressing bug, rather than the per-platform trait implementations.

Jeff, Alexis, could you confirm that you only see the bug if gfx.webrender.compositor is enabled? If that's the case, I don't need to look at this right away this morning.

I haven't seen this since turning off gfx.webrender.compositor and saw it pretty often with it on. So I think we can assume that it's gfx.webrender.compositor only.

Yep, same.

I need to do some more testing with this to verify it's a valid hack / workaround. If there are any other issues, I'll just back out the original patch, for now.

(In reply to Glenn Watson [:gw] from comment #10)

I need to do some more testing with this to verify it's a valid hack / workaround. If there are any other issues, I'll just back out the original patch, for now.

It seems to work OK for me, and I think this patch should fix all cases of this.

The new build seems to work for me too.

Turns out I didn't turn on gfx.webrender.compositor in the new build :)

I'm able to reliably reproduce the problem by scrolling down to the sample image on https://docs.rs/raqote/0.7.6/raqote/. I can not reproduce the problem in the new build with gfx.webrender.compositor turned on.

https://hg.mozilla.org/mozilla-central/rev/2dd771769da7

I've reproduce this issue with Fx 72.0a1(2019-12-18) on macOS 10.15 (MacBook Pro).
The issue is verified fixed with Fx 74.0a1(2020-02-01) and Fx 73.0b12 on macOS 10.15 and Windows 10.