In bug 1385733 I'm trying to use insertTree in place of insert for inserting a folder. browser_bookmarkProperties_addFolderDefaultButton.js was failing as the folder was getting inserted in the wrong position, even though the index was being passed to insertTree. For now, PT.NewFolder includes an extra update after insertion to set the correct index.
The risk is that a consumer passes bogus indices, that's also the reason it doesn't pick indices iirc.
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