User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:61.0) Gecko/20100101 Firefox/61.0 Build ID: 20180607135512 Steps to reproduce: From Firefox 61.0b9 a tab with probably any page crashes after short time. It takes minutes or max. tens of minutes to crash again. No specific pages or actions to reproduce. It was OK in 61.0b8 but no change for better since then. I add one crash report for all from 61.0b12 https://crash-stats.mozilla.com/report/index/f68087b1-9566-4a6d-8f76-7cb550180611 All the crashes have the same reason "Item found was in the wrong list! type 54 (outer type was 38 at depth 3, now is 69)".

I am sorry for commenting a closed bug. Marek, can you please try this binary if you still reproduce the crash reliably? (I assume you are using win64) https://queue.taskcluster.net/v1/task/W6w4rB7-STWzMuQpo5Hy3g/runs/0/artifacts/public/build/target.zip A suspicious change I can think of between b8 and b9 is bug 1462497. I start thinking that part 1 and 2 of the patches fixed some crashes, but part 3 and 4 introduced new crashes such as this bug. So the binary above doesn't include those part 3 and 4 patches.

It's weekend so not much testing but so far I can say it solved the problem for me and it doesn't crash any more.

Thank you, Marek! I filed bug 1469220 for the backout.

I'd like just to add that the problem with crashes disappeared in 61.0b14 for me. So if changes in bug 1469220 were applied between b13 and b14 (I'm sorry I don't know how to find it out), I can confirm it works. Otherwise it would seem the problem was caused by something different.

Bug 1469220 has been landed on beta but any new versions of the beta haven't been released since then. The change between b13 and b14 is that retained display list has been disabled in beta channel; https://hg.mozilla.org/releases/mozilla-beta/rev/4b525127bb53