We have recently noticed StructureID memory usage issues, including leaks and larger numbers of StructureIDs than one would expect. This is a master bug to track these issue.
As a starting point, we currently allocate 142 StrucutureIDs for about:blank.
(In reply to comment #1) > As a starting point, we currently allocate 142 StrucutureIDs for about:blank. Oops. That comment was meant for bug 21683.
Child bugs of this umbrella all resolved.