I think it is okay to allow OBJECT for http:// on the safer level as well as there is a special permission fetch which is used for object_subrequest and which is not enabled for http:// on the safer level. Thus, it should prevent loading scripts from http:// sources behind OBJECT elements.
Trac: Cc: N/Ato arthuredelstein Keywords: N/Adeleted, TorBrowserTeam201809R added Status: new to needs_review