See: https://bugzilla.mozilla.org/show_bug.cgi?id=1594345

The consensus there appears to be that, while we treat the history updates as deferred/promises, we don't actually handle them that way. We may need to do some research to sort out whether browsers other than FF/Chrome will respect this kind of handling, and work around otherwise. We could potentially solve this by "simply" adding another browser-specific hack.