This bug was filed from the Socorro interface and is report bp-ec45341c-bf24-4127-9d98-a55410170706. ============================================================= There is 1 crash in nightly 56 with buildid 20170706030206. In analyzing the backtrace, the regression may have been introduced by patch  to fix bug 1376855.  https://hg.mozilla.org/mozilla-central/rev?node=47c66f214de35be5b863c1431abdd467794ef44e
Sorry for late reply, I'll keep tracking this bug. Thanks for report.
WebRender is non on by default.
There's a bunch of these crashes without WR enabled, on 52 ESR branch. There's only 4 with WR enabled, on 56/57. The most recent is at https://crash-stats.mozilla.com/report/index/e20ed0a1-3ad8-4482-ab67-014310170806, buildid 20170805100334 which is a month and a half ago. I think it's safe to close; we can reopen if it shows up again.