70mb or so of the heap-unclassified in bug 291643 looks like it is from mSlots, which is a data structure uniquely owned by a node. Slots are not supposed to be common, but in unusual cases they are used. I think Shadow DOM will use them more, so it would be good to have reporting for them. Note this may not actually help reduce the heap-unclassified in bug 291643, because I also see a lot of nodes in there, so maybe the slots are for nodes we aren't reporting for whatever reason. Since bug 795128, FragmentOrElement does measure nsDOMSlots (a subclass of slots), so maybe this is just a problem for less common nodes. (There's also an additional subclass, nsDataSlots.)

Yeah, I bet the slots aren't being reported just because a bunch of HTML elements are being reported.

khuey points out that "are being reported" should be "are not being reported".

https://bugzilla.mozilla.org/show_bug.cgi?id=1472046 Move all DOM bugs that haven’t been updated in more than 3 years and has no one currently assigned to P5. If you have questions, please contact :mdaly.