I ran mozregression to find the fix range. In old builds (e.g. comment 0's datestamp) I'm not seeing anything as bad as the 50-second time that I mentioned in comment 0 -- I'm seeing something like 5-6 seconds in newer builds vs. 8-12 seconds in older builds (with noticeably smaller progression per frame towards the end). But that was still enough to find a fix range: https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=b47dc08fc77ad2f26cee89a216c333ff490d195f&tochange=c6d819bd39daf86acd5e0c5bce5d74c2db8b8d64 That includes bug 1682623 "Enable Warp Compiled Generators and Async Functions", which sounds like it'd be what fixed this, based on comment 2.
Bug 1552356 Comment 5 Edit History
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I ran mozregression to find the fix range. In old builds (e.g. comment 0's datestamp) I'm not seeing anything as bad as the 50-second time that I mentioned in comment 0 -- I'm seeing something like 5-6 seconds in newer builds, maybe 6-7 seconds in Chrome, vs. 8-12 seconds in older Firefox builds (with noticeably smaller progression per frame towards the end). But that was still enough to find a fix range: https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=b47dc08fc77ad2f26cee89a216c333ff490d195f&tochange=c6d819bd39daf86acd5e0c5bce5d74c2db8b8d64 That includes bug 1682623 "Enable Warp Compiled Generators and Async Functions", which sounds like it'd be what fixed this, based on comment 2.