This is a serious bug.
https://twitter.com/tobiasbu/status/1378131506661560322

1. Go to https://codepen.io/tobias_buschor/pen/ExZmygP
2. Hover

Expected:
Look at the animation

Actual:
Animation starts then freezes the full browser with a maxed out CPU.

You need to force restart the browser to be able to use it.

Running mozregression gives this range
https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=ff1a0c64ae96ab64fd2a88b23a24b9cf0e53fe2e&tochange=1b9d508de57519880036fdf48473d007f1c31e0a

tested on macos

Though it's strange because Bug 1516056 is just a comment change.
Or did I miss something in the regression range or the crash is random?

The other changeset in the range might be a problem? https://hg.mozilla.org/integration/autoland/rev/1b9d508de57519880036fdf48473d007f1c31e0a, this has mac specific changes.

Could someone run a regression window on Windows just to see if it's macos only?

I get

https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=43481dc46b3887619894fbe07da42e0a619021d3&tochange=96cd358e3eedc981b0bf4e00294ed73ce099d1c0

on mac, which indicates it's likely a webrender bug. I'll check with webrender force enabled next.

https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=e5474686074d42938961abf399cb3bff1f7b6487&tochange=1b2acec8316617e5ce2972b66e11d0955bfd72e7

-> bug 1624468

(In reply to Timothy Nikkel (:tnikkel) from comment #5)

https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=e5474686074d42938961abf399cb3bff1f7b6487&tochange=1b2acec8316617e5ce2972b66e11d0955bfd72e7

-> bug 1624468

(I get the same regression range on Linux with WR prefed on.)

https://hg.mozilla.org/mozilla-central/rev/cbd0383b5719

Please nominate this for Beta approval.

Comment on attachment 9214024 [details]
WIP: Bug 1703141 - Prevent infinite loop in gradient fast-path.

Beta/Release Uplift Approval Request

• User impact if declined: infinite loop causing freezes
• Is this code covered by automated tests?: No
• Has the fix been verified in Nightly?: Yes
• Needs manual test from QE?: No
• If yes, steps to reproduce:
• List of other uplifts needed: None
• Risk to taking this patch: Low
• Why is the change risky/not risky? (and alternatives if risky): Simple fix.
• String changes made/needed: None.

Comment on attachment 9214024 [details]
WIP: Bug 1703141 - Prevent infinite loop in gradient fast-path.

Approved for 88.0b9, thanks. Can we land a crashtest for this?

https://hg.mozilla.org/releases/mozilla-beta/rev/e7933680c43b

I was able to reproduce the issue on Firefox 89.0a1 (2021-04-05) under macOS 11.2.3 by using the links from Comment 0.

The issue is fixed on Firefox 88.0b9 and Firefox Nightly 89.0a1 (2021-04-11). Tests were performed on macOS 11.2.3, Windows 10 and Ubuntu 20.04.

https://hg.mozilla.org/mozilla-central/rev/abe8316b5a90