This issues was around `manager` getter which triggers this assertion anytime we access it after the JS Process Actor has been unregistered. There must be something wrong in that getter, which may be correct on JSWindowActor, but not on JSProcessActor.
Bug 1918267 Comment 9 Edit History
Note: The actual edited comment in the bug view page will always show the original commenter’s name and original timestamp.
This issue was around `manager` getter which triggers this assertion anytime we access it after the JS Process Actor has been unregistered. There must be something wrong in that getter, which may be correct on JSWindowActor, but not on JSProcessActor.