Seth and I were talking when dealing with Bug 363024 and realized that a lot of other components might easily have the same problem. We should make a test-case that iterates through all of registered components and calls createInstance on them twice. We shouldn't crash.
Is this related to bug 181491?
It could be - not 100% sure though.
Joey - aren't you doing something like this for thunderbird and null parameters?
Yes. See bug 412109, which includes a readily adaptable script.
Myk - you seem to be doing lots of work with things to help out add-ons, and this is one of those things that helps prevent them from shooting themselves in the foot. You might want to take a look at this.