dbaron writes in 51777 - "Erm... I *think* this is a very basic problem. I think (based on a quick look at the code) that we leak the document whenever a document is used through JS to create an element that is not added to that document's content model. (I'm surprised we didn't see this earlier.) I have to look and see whether we set the document to null on creation, or whether we use the document whose factory method is being used. If the former, this could be easy to fix, although it means sacrificing persistence of user- decorated properties on elements before they are added to the document, in some cases."

Chris, I don't know if it's a general dom1 problem or specific to XUL - it's an nsXULDocument that's getting leaked so I'm taking a guess and assigning it to you (sorry :-( ) cc'ing dbaron if he has thoughts on a better assignment.

Well, we both filed this about the same time. I'm going to mark this a duplicate of the other rather than repeat myself... *** This bug has been marked as a duplicate of 52726 ***

verified as dup.