Sounds very similar to https://bugzilla.mozilla.org/show_bug.cgi?id=1618546. I have a potential patch uploaded there.
Bug 1622429 Comment 2 Edit History
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Sounds very similar to https://bugzilla.mozilla.org/show_bug.cgi?id=1618546. I have a potential patch uploaded there. Edit: Even if the root cause is the same as Bug 1618546, I think we should still make the debugger more reliable in case service worker debugging throws.