Is this still reproducing on latest Firefox versions? e.g Firefox 43 If yes, could you provide a detailed test case so we can use to reproduce the issue?
Yes, this still happens in nightly. Perhaps the simplest way to reproduce is to take any addon with a preferences dialog window, open the preferences dialog, open DOM Inspector, and manually remove any preference element from inside the preferences container. The typeError will be thrown.
I see that per comment 2.
Status: UNCONFIRMED → NEW
Component: Untriaged → XUL Widgets
Ever confirmed: true
OS: Linux → All
Product: Firefox → Toolkit
Hardware: x86 → All
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