Interestingly, the test doesn't work when hosted on the web (i.e.., with content principal). Maybe there's a problem with the nullprincipal that the data URL gets? I wonder what happens with iframe sandbox...
Bug 1644076 Comment 1 Edit History
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~Interestingly, the test doesn't work when hosted on the web (i.e.., with content principal). Maybe there's a problem with the nullprincipal that the data URL gets? I wonder what happens with iframe sandbox...~