mozregression got me down to https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=c68fe15a81fc2dc9fc5765f3be2573519c09b6c1&tochange=567a8768593eb06a86deb263f94d9de2d3d3e8fa Bug 1642594 looks possibly relevant.
Bug 1739923 Comment 4 Edit History
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mozregression got me down to https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=c68fe15a81fc2dc9fc5765f3be2573519c09b6c1&tochange=567a8768593eb06a86deb263f94d9de2d3d3e8fa Bug 1642594 looks possibly relevant. EDIT: Hrm, only on Windows apparently. In my Linux VM, this crashes basically since ever.