Ok, looking into this more... Our metrics started showing a spike in NACKs around October 14th. These NACKS indicate (code: 302) that there was a problem with the UserAgent sending the Push Message content to the [ServiceWorker](https://developer.mozilla.org/en-US/docs/Web/API/ServiceWorker). (Which is a little bit of Javascript that the site installs which figures out what to do with the incoming message, usually just popping up that "[Notification](https://developer.mozilla.org/en-US/docs/Web/API/Notification)" DOM element.) Firefox has no insight into what might be causing the serviceworker to fail, but it is a bit odd that it started the day after 131.0.3 rolled out. (For folk that want to play along at home: https://searchfox.org/mozilla-central/source/dom/serviceworkers/ServiceWorkerOp.cpp#193 handles the service worker response which goes to https://searchfox.org/mozilla-central/source/dom/serviceworkers/ServiceWorkerOp.cpp#137 https://searchfox.org/mozilla-central/source/dom/serviceworkers/ServiceWorkerOp.cpp#727 which gets translated to https://searchfox.org/mozilla-central/source/dom/push/PushServiceWebSocket.sys.mjs#40 which gets send as part of the NACK.) That's about the best I can do.
Bug 1925631 Comment 6 Edit History
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Ok, looking into this more... Our metrics started showing a spike in NACKs around October 14th. These NACKS indicate (code: 301 & 302) that there was a problem with the UserAgent sending the Push Message content to the [ServiceWorker](https://developer.mozilla.org/en-US/docs/Web/API/ServiceWorker). (Which is a little bit of Javascript that the site installs which figures out what to do with the incoming message, usually just popping up that "[Notification](https://developer.mozilla.org/en-US/docs/Web/API/Notification)" DOM element.) Firefox has no insight into what might be causing the serviceworker to fail, but it is a bit odd that it started the day after 131.0.3 rolled out. (For folk that want to play along at home: https://searchfox.org/mozilla-central/source/dom/serviceworkers/ServiceWorkerOp.cpp#193 handles the service worker response which goes to https://searchfox.org/mozilla-central/source/dom/serviceworkers/ServiceWorkerOp.cpp#137 https://searchfox.org/mozilla-central/source/dom/serviceworkers/ServiceWorkerOp.cpp#727 which gets translated to https://searchfox.org/mozilla-central/source/dom/push/PushServiceWebSocket.sys.mjs#40 which gets send as part of the NACK.) That's about the best I can do.