Do not mistake Gnash as proprietary Adobe Flash and disable it. The Gnash binary is run out of process and uses XEmbed. Hence it does not matter from Epiphany's perspective what version of Gtk+ it uses.

There are various different ways to do this:
1. Check the libraries that the plugins link to.
2. Look for Gnash in the plugin's description.
3. Check the name of the shared object.

(1) won't work because the proprietary Adobe Flash uses dlopen to look for Gtk+ 2.x and then 1.x.

(3) won't work because I don't have a recent enough WebkitGtk+ with webkit_web_plugin_get_path, and I can not wait for a new release. :-)

(2) is what is proposed in https://bugzilla.mozilla.org/516166 The only problem is that people might change the description (can be done via an environment variable) to be an exact copy of Adobe's to satisfy stupid Flash detection scripts (http://cgit.freedesktop.org/swfdec/swfdec-mozilla/commit?id=2ff383). But then some of these stupid Web sites (eg., iMeem) are now dead.