This fix has been verified on firefox66 as well using the procedure as the one in comment 28. The issue has reproduced on an affected Beta 10 build and it did not occur anymore after updating to the latest Beta 11. This bug is not fully verified. Thank you for your contribution!
Bug 1515088 Comment 36 Edit History
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This fix has been verified on firefox66 as well using the procedure as the one in comment 28. The issue has reproduced on an affected Beta 10 build and it did not occur anymore after updating to the latest Beta 11. This bug is now fully verified. Thank you for your contribution!