As reported in mozillaZine by JoeG, Insert List of Extensions is a little buggy.
Problem is that there are too much callback in nightly.getExtensionList().
There was a misplacing in harth's commit.
Issue #88 - no looping callback in getExtensionList() with Gecko 1.9.x.
Fixed by 10c8fa9 in #89.
Target Milestone is 3.4.
@whimboo would You mind to set it?