I think this is just the interaction with the slow script dialog. The message being run when the slow script dialog fires will be delayed until the dialog is closed.
Hi Kyle, I still think this is a wrong behavior and I stated my reasoning below. Hope to see your input soon. I am not sure if the semantics of "messages should be received on the other side in the order of being sent by postMessage()" is defined in the web worker's spec. I'd guess that most of programmers will expect that in normal situations. When it comes to the slowness I'd expect some adjustments like: 1) If a message is slow, all messages after it should wait. 2) If a message is slow and a slow script dialog is being displayed, all messages after it should still wait until either of followings: 2.1) User clicked on Stop script: the message should be discarded, rest of messages continue as usual. This may break the program but user is aware of it. 2.2) User clicked on Continue: then all messages continue to wait until the the message finally arrives or case 2.1 happens on another dialog (I am assuming a slow dialog will display again repeatedly at a certain interval).
Verified that it is still happening in version 13.0.1. However it is less frequent than in version 12. I had to wait for a couple of minutes to see it happen. Version info: Mozilla/5.0 (X11; Ubuntu; Linux i686; rv:13.0) Gecko/20100101 Firefox/13.0.1