Talos has detected a Firefox performance regression from push:

https://hg.mozilla.org/integration/autoland/pushloghtml?changeset=c9c63f8447027d14ec2c541e82aae1014f08f812

As author of one of the patches included in that push, we need your help to address this regression.

Regressions:

19% tart linux64-shippable opt e10s stylo 2.20 -> 2.62
6% tart linux64-shippable-qr opt e10s stylo 3.50 -> 3.72

You can find links to graphs and comparison views for each of the above tests at: https://treeherder.mozilla.org/perf.html#/alerts?id=23337

On the page above you can see an alert for each affected platform as well as a link to a graph showing the history of scores for this test. There is also a link to a treeherder page showing the Talos jobs in a pushlog format.

To learn more about the regressing test(s), please see: https://wiki.mozilla.org/TestEngineering/Performance/Talos

For information on reproducing and debugging the regression, either on try or locally, see: https://wiki.mozilla.org/TestEngineering/Performance/Talos/Running

*** Please let us know your plans within 3 business days, or the offending patch(es) will be backed out! ***

Our wiki page outlines the common responses and expectations: https://wiki.mozilla.org/TestEngineering/Performance/Talos/RegressionBugsHandling

This seems to be the cost of the megabar animation, which cannot run on the compositor. Short of going with a visibly different kind of animation, I don't think there's much we can do here.

Bug 1586232 appears to have fixed this.