One really nice thing would be if GeckoResult could track where it was created so that if it eventually gets rejected the stacktrace contains the full stack (and not just the last piece) E.g.

05-13 14:03:37.047 31773 31773 E AndroidRuntime: java.lang.IllegalStateException: result is already complete
05-13 14:03:37.047 31773 31773 E AndroidRuntime: 	at org.mozilla.geckoview.GeckoResult.complete(GeckoResult.java:795)
05-13 14:03:37.047 31773 31773 E AndroidRuntime: 	at org.mozilla.geckoview.WebExtensionController$WebExtensionResult.sendSuccess(WebExtensionController.java:431)
05-13 14:03:37.047 31773 31773 E AndroidRuntime: 	at org.mozilla.gecko.EventDispatcher$JavaCallbackDelegate$1.run(EventDispatcher.java:452)
05-13 14:03:37.047 31773 31773 E AndroidRuntime: 	at android.os.Handler.handleCallback(Handler.java:790)
05-13 14:03:37.047 31773 31773 E AndroidRuntime: 	at android.os.Handler.dispatchMessage(Handler.java:99)
05-13 14:03:37.047 31773 31773 E AndroidRuntime: 	at android.os.Looper.loop(Looper.java:164)
05-13 14:03:37.047 31773 31773 E AndroidRuntime: 	at android.app.ActivityThread.main(ActivityThread.java:6494)
05-13 14:03:37.047 31773 31773 E AndroidRuntime: 	at java.lang.reflect.Method.invoke(Native Method)
05-13 14:03:37.047 31773 31773 E AndroidRuntime: 	at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
05-13 14:03:37.047 31773 31773 E AndroidRuntime: 	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)

This stacktrace would continue with where the GeckoResult was created.

Tasks should have severity N/A.