If I'm right about this bug being fundamentally a problem with system resources, turning on webrender should make the crashes happen much more often. But they're so intermittent that it'd be hard to tell this was happening. The stacks might be different, but I doubt that would tell us much -- the crashes would still happen deep in macOS code. On balance, I suspect it's not worth your trouble trying to test with webrender on.
Bug 1576767 Comment 218 Edit History
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If I'm right about this bug being fundamentally a problem with system resources, turning on webrender should make the crashes happen much more often. But they're so intermittent that it'd be hard to tell this was happening. The stacks might be different, but I doubt that would tell us much -- the crashes would still almost certainly happen at the same location deep in macOS code. On balance, I suspect it's not worth your trouble trying to test with webrender on.