__define{Getter,Setter}__ are deprecated, and are not defined on
NonSyntacticVariablesObjects, so these calls get in the way of sharing
globals between different .jsms. Probably only the DownloadUtils.jsm
change is really needed for that.
configurable and enumerable are both set to true to match the existing
behavior. If enumerable is set to false, then tests fail, because some
of the getters overwrite the getter with a regular property.
MozReview-Commit-ID: 1OZF45fIAQ
5e5e5b9abb