I also come across this. I see this on your demo site above for each request, but also see it on one of my sites. I didnโt notice this before, and Iโm sure I would notice it, because every day I look at the console. Gives pretty mixed messages.

I am using mac with firebug 1.5. This error is reported in the error list firebug id = 2712, but it seems that it will not go anywhere. It's complicated. As a rule, I notice this when I have two simultaneous requests at the same time, and perhaps one proactively returns before the other. But this should not cause an error message.
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