Firefox 17-26 iterators throw a StopIteration object to indicate "done". This normalizes it.
^1.3.0
^1.1.0
^0.17.1
^21.1.1
^0.2.2
^5.6.5
^2.5.0
^0.1.13
=8.8.0
^2.0.1
^0.3.1
^10.3.2
^2.0.0
^5.9.0
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