Since Firefox 52, the Wikipedia icon (favicon) is rendered incorrectly : there are two points above each side of the W. To reproduce: open https://www.wikipedia.org and check the tab icon. Works in Firefox 51, broken in Firefox 52. Regression window: https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=8002299dfc3fb3b2c53e50e40a8e16f8dff2c3e7&tochange=c44c01dfd264370c1558b747525d220a9a89b51c

Cannot reproduce in Firefox 56 on Fedora 27.

Hmm, I get a different regression range https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=3587b25bae302c1eed72968dbd7cef883e715948&tochange=efe7d026ac641759838dd3897c37892e37e5b244

(In reply to Timothy Nikkel (:tnikkel) from comment #2) Here's an excerpt of mozregression: C:\Users\Utilisateur>mozregression -g 51 -b 52 0:00.15 INFO: bits option not specified, using 64-bit builds. 0:00.15 INFO: Using date 2016-11-14 for release 52 0:00.18 INFO: Using date 2016-09-19 for release 51 So I can't see how it could narrow it down to between 2016-03-22 and 2016-03-23. By the way, here's the narrower window given by the command line version: https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=a7c654513f2ffd9d9ef38fa2bf512b9e8dae3cdd&tochange=c44c01dfd264370c1558b747525d220a9a89b51c

Ah, I think I understand this now. If I apply my patch from bug 1404366 that fixes the problem. So the non-premultiplied data must be causing this. In my regression range is Bug 1207332. Enable skia content on OS X. and I'm on OS X. skia doesn't handle non-premultied data as well as cairo did. In your regression range there is Enable the GPU process for Nightly Windows users. (bug 1314133 which seems plausible for changing how non-premultied data is handled.

That's great news! Let's hope it fixes it on Windows too.

Is this gone now that bug 1404366 is fixed?

It's better (see screenshot) but not yet fixed.

I think that is an artifact of using high quality downscaling on a 1-bit alpha mask (so we get alpha values other than 0 and 255) on an image that is designed to expect only 0 or 255 alpha. Perhaps we should just turn off downscaling of ICOs that have an AND mask?