You can clone with
I have just tested Shumway on a site and saw no flash content.
This was caused by the site using a Flash detection script that checked
to ensure a compatible version of Flash could be found.
I'm not sure what can be done about this as the plugins collection is read-only. The only thing that leaps to mind is having a dummy plug-in that has a name of Shockwave Flash, but that seems messy
Similar to https://bugzilla.mozilla.org/show_bug.cgi?id=840439