I did some debugging on local layout tests, and I have some leak fixes for WebKit and DumpRenderTree.
Created attachment 11597 [details] patch that fixes some leaks I can reproduce locally
Besides these leaks, I can reproduce some others that seem to be caused by NSHTMLReader code used when doing the copy operation -- I haven't figured out how to fix those yet.
Comment on attachment 11597 [details] patch that fixes some leaks I can reproduce locally r=me
Committed revision 17871.
Bug 11236 is related to the NSHTMLReader leaks.