(applying the issue from comment 15 to what-was-described-in-comment 0 here: maybe user completes the print operation really quickly, and `EnumeratePrinters` was somehow either still pending or still continuing in the background; and when the print operation completes, the `nsDeviceContextSpecGTK` gets torn down, despite the fact that `EnumeratePrinters` is still running.)
Bug 1660223 Comment 19 Edit History
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(applying the issue from comment 15 to what-was-described-in-comment 0 here: maybe the user completes the print operation really quickly, and `EnumeratePrinters` was somehow either still pending or still continuing in the background (not sure if it strictly must complete before the print UI is usable?); and when the print operation completes, the `nsDeviceContextSpecGTK` gets torn down, despite the fact that `EnumeratePrinters` is still running.)