bug 1848278 is going to make the permanent atom extensible from embedder, and which allows optimizing CreateInterfaceObject and some other atom-related operation.
with speedometer 3, the 30% of the time taken by CreateInterfaceObject is atomization, and that part can be moved to compile-time (hash and length calculation, getter/setter name calculation) + startup (remaining atomization operation into permanent atoms)

WIP patch stack: https://treeherder.mozilla.org/jobs?repo=try&revision=5d0a314f90f54b4197a10a6cf03df150c8b10be5