User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:99.0) Gecko/20100101 Firefox/99.0

Steps to reproduce:

Using FF 99.0.1 64bit on W10 20H2 64bit.
Created sample HTML with pulsating drop shadow for simple box. See attachment.

Actual results:

CSS drop-shadow transition is very jerky, jumpy and not smooth at all.

Expected results:

CSS drop-shadow transition should be as smooth as in Chrome or Edge.

The Bugbug bot thinks this bug should belong to the 'Core::CSS Parsing and Computation' component, and is moving the bug to that component. Please correct in case you think the bot is wrong.

15:45.40 INFO: Last good revision: 8e9c1ffdeed84e460a9ba7f9e83ca24319a15c87
15:45.40 INFO: First bad revision: b7f88e5c537bb7d64ba9d4cb58b052650d510638
15:45.40 INFO: Pushlog:
https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=8e9c1ffdeed84e460a9ba7f9e83ca24319a15c87&tochange=b7f88e5c537bb7d64ba9d4cb58b052650d510638

This appears to be fixed for me in current nightly (which will be from bug #1765013). Are you able to verify? (the patch was also uplifted to beta).

Still seeing this in the latest Nightly

Set release status flags based on info from the regressing bug 1749380

Left is FF 99.0.1
Middle is FF 101.0a1 -> "seems" to be little better
Right is GC 100.0.4896.127 -> smooth and nice

Checked now with:

• FF 99.0.1 (of course still not smooth)
• FF 101.0a1 (seems a little better)
• GC 100.0.4896.127 (smooth and nice)

See above attachment "drop-shadow_FF99_FF101_GC.wmv"

"Real life" example hier on my site: https://www.tr1.de/pages/forum.php
Check the "Register" button on the top-right.

Not related to this but I've seen the below issue while debugging the drop-shadow bug:

If keyframes are defined with 0: instead of 0%:, it works in the browser but the 0%: rule is not displayed in the CSS rule view from the FF developer tools. In my case only the 50%: and 100%: rules are shown. That might be a bug.

I'm using since ages the YUI Compressor (https://yui.github.io/yuicompressor/) which optimizes the 0%: to a 0: ...

Thanks for the bug report manfred. Could you please try taking a performance profile. Go to profiler.firefox.com and follow the instructions to install. In the drop down menu this installs in your toolbar please select "Graphics" under the settings. Then press ctrl+shift+1 to start capturing and ctrl+shift+2 to stop. This should open a new tab with the profile, and in the top-right there will be a "Upload local profile" button. Please click that then share the URL here. If you need any help with that please let me know. Thanks!

Hope I did it correct:
https://share.firefox.dev/3y0bECM

That's great, thanks.

The profile looks fine. I was mistaken, this isn't actually a performance issue but something about the rendering of the animation that makes it look jumpy

Set release status flags based on info from the regressing bug 1749380

With FF 100.0 I can't see the bug anymore at the button from my website. See above comment 9: "Real life" example...
But with the attached .html file, there is still a small jumping of the shadow. Much better than before but not gone.

This was not fixed by bug 1768678. I can still repro in the latest nightly