I think this is the same issue as in bug 159224 comment 6, but we'd have to confirm. The fact that it only started happening recently for you on nightly means maybe there's a slightly different scenario here. First of all check what the value of `network.trr.mode` is for you. Then please run mozregression to find the change that introduced this problem. Eventually we may need you to also gather some [HTTP logs](https://developer.mozilla.org/en-US/docs/Mozilla/Debugging/HTTP_logging) to see exactly what's happening.
Bug 1640091 Comment 3 Edit History
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I think this is the same issue as in bug 1592248 comment 6, but we'd have to confirm. The fact that it only started happening recently for you on nightly means maybe there's a slightly different scenario here. First of all check what the value of `network.trr.mode` is for you. Then please run mozregression to find the change that introduced this problem. Eventually we may need you to also gather some [HTTP logs](https://developer.mozilla.org/en-US/docs/Mozilla/Debugging/HTTP_logging) to see exactly what's happening.