Talos has detected a Firefox performance regression from push: https://hg.mozilla.org/integration/autoland/pushloghtml?changeset=6a9f15fb809da3bed50ede05e663537c44075778 As author of one of the patches included in that push, we need your help to address this regression. Regressions: 4% about_preferences_basic linux64 opt e10s stylo 148.71 -> 154.81 4% about_preferences_basic windows7-32 opt e10s stylo 138.03 -> 143.57 4% about_preferences_basic windows10-64 opt e10s stylo 139.11 -> 144.45 4% about_preferences_basic windows10-64-qr opt e10s stylo 139.08 -> 143.99 3% about_preferences_basic osx-10-10 opt e10s stylo 207.52 -> 214.27 3% about_preferences_basic windows7-32 pgo e10s stylo 125.55 -> 128.91 You can find links to graphs and comparison views for each of the above tests at: https://treeherder.mozilla.org/perf.html#/alerts?id=17663 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/Performance_sheriffing/Talos/Tests For information on reproducing and debugging the regression, either on try or locally, see: https://wiki.mozilla.org/Performance_sheriffing/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/Performance_sheriffing/Talos/RegressionBugsHandling

I'll soon post the Gecko profiles.

Here are the Gecko profiles for about_preferences_basic on Windows 10 OPT builds: before: https://perf-html.io/from-url/https%3A%2F%2Fqueue.taskcluster.net%2Fv1%2Ftask%2FMKjqiqZzQLOFlGe5dY9YiA%2Fruns%2F0%2Fartifacts%2Fpublic%2Ftest_info%2Fprofile_about_preferences_basic.zip after: https://perf-html.io/from-url/https%3A%2F%2Fqueue.taskcluster.net%2Fv1%2Ftask%2FJ63JfkGATVSugtJywOWY5Q%2Fruns%2F0%2Fartifacts%2Fpublic%2Ftest_info%2Fprofile_about_preferences_basic.zip For about_preferences_basic on OS X: before: https://perf-html.io/from-url/https%3A%2F%2Fqueue.taskcluster.net%2Fv1%2Ftask%2FE-dfoOBYQM-pmQb2cSnh8A%2Fruns%2F0%2Fartifacts%2Fpublic%2Ftest_info%2Fprofile_about_preferences_basic.zip after: https://perf-html.io/from-url/https%3A%2F%2Fqueue.taskcluster.net%2Fv1%2Ftask%2FaKu4NSS6Tu-ZbJaoYQB7gA%2Fruns%2F0%2Fartifacts%2Fpublic%2Ftest_info%2Fprofile_about_preferences_basic.zip

Thanks, forwarding the needinfo to johannh to make the call on this.

Thanks to Ehsan's help with correctly understanding those profiles we may have a chance at fixing (and potentially improving) perf here. The main culprit seems to be this call to .focus() https://searchfox.org/mozilla-central/rev/876022232b15425bb9efde189caf747823b39567/browser/components/preferences/in-content/findInPage.js#28 which causes a full XUL layout and seems to be getting slower and slower the more XUL we add to this file. I'm going to try and remove it in favor of an html input with an autocomplete tag and do a talos run. Local profiler results are promising: https://perfht.ml/2FBTygT

Any updates here? Also :johannh, if you filed a separate bug for this issue, please link it here.

We've decided to accept this regression. We need the UI changes that this patch brought, and the negative effect is small enough to accept.