This is a Beta-only bug to set layout.display-list.retain to false in FF61 beta and release: https://searchfox.org/mozilla-central/source/gfx/thebes/gfxPrefs.h#673

Approval Request Comment [Feature/Bug causing the regression]: Retained display lists [User impact if declined]: Unable to perform a staged rollout as intended [Is this code covered by automated tests?]: Yes [Has the fix been verified in Nightly?]: No, this is Beta-only. Try pushes have been done to confirm no CI issues and QA has done manual smoketesting of those builds to confirm that nothing breaks with RDL off. [Needs manual test from QE? If yes, steps to reproduce]: Yes, we should verify that the feature is disabled as expected in 61.0b14. [List of other uplifts needed for the feature/fix]: None [Is the change risky?]: Minimally [Why is the change risky/not risky?]: Reverts us to the Fx60 state of things. Smoketesting and automated tests of the disabled condition haven't revealed any obvious issues. [String changes made/needed]: None

Comment on attachment 8985109 [details] [diff] [review] pref off RDL Approved for 61.0b14.

Hello guys, We have verified that layout.display-list.retain pref is set to false by default on Firefox 61.0b14(20180614135649) on Windows 10 64bit, macOS 10.13 and Ubuntu 16.04 64bit. And considering the testing we had in 2018-06-07 on the RDL(preffed-off) build in which we encountered no issues, we can confirm this issue as verified-fixed.

Seems like this bug brought back AWSY perf: == Change summary for alert #13875 (as of Wed, 13 Jun 2018 10:56:21 GMT) == Improvements: 6% Heap Unclassified windows7-32-nightly opt stylo 33,803,207.19 -> 31,683,438.59 6% Heap Unclassified windows10-64-nightly opt stylo 41,426,716.84 -> 38,865,161.68 5% Heap Unclassified macosx64-nightly opt stylo 73,077,222.76 -> 69,419,138.08 3% Heap Unclassified linux64-nightly opt stylo 55,875,174.89 -> 54,077,529.11 For up to date results, see: https://treeherder.mozilla.org/perf.html#/alerts?id=13875

now that firefox 62 is on beta, we have a regression since this had an improvement for 61 only: == Change summary for alert #14026 (as of Sun, 24 Jun 2018 02:41:50 GMT) == Regressions: 6% Heap Unclassified windows7-32-nightly opt stylo 31,718,536.83 -> 33,566,270.77 6% Heap Unclassified windows10-64-nightly opt stylo 39,252,440.21 -> 41,528,360.07 For up to date results, see: https://treeherder.mozilla.org/perf.html#/alerts?id=14026

For firefox 61 I also noticed this improvement: == Change summary for alert #14088 (as of Fri, 29 Jun 2018 04:16:52 GMT) == Improvements: 2% tsvgx linux64 opt e10s stylo 178.94 -> 175.25 For up to date results, see: https://treeherder.mozilla.org/perf.html#/alerts?id=14088

But for firefox 62 we remained with the regression: == Change summary for alert #13982 (as of Mon, 18 Jun 2018 18:43:20 GMT) == Regressions: 2% tsvgx linux64 opt e10s stylo 175.20 -> 179.33 For up to date results, see: https://treeherder.mozilla.org/perf.html#/alerts?id=13982