What is the NS_ERROR_INVALID_POINTER error in Firefox?

Question

While testing JavaScript code in Firefox 3.5 I sometimes get the following error:

Component returned failure code: 0x80004003 (NS_ERROR_INVALID_POINTER)
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Answer 1

I just had the error by mistakenly trying to append an element to itself: elem.appendChild(elem);

Answer 2

Without knowing specifically what you are calling, the error generally means you've passed something null to something that does not expect a null value.

Answer 3

I had this error too using Coffeescript when my Callback functions were defined after my main function. I just had to re order my functions to make it work. Hope it helps.