Flash doesn't work on Firefox with GTK3

[Eugene Barsukovsky]

Dear Gecko team,

I built www/firefox from ports (ports tree is up to date) with default options except for setting toolkit to GTK3,
then installed www/linux-c6-flashplugin11, and it doesn't work. plugin_container crashes when I ty to load
a page containig flash video with error
(<unknown>:21560): Gtk-ERROR **: GTK+ 2.x symbols detected. Using GTK+ 2.x and GTK+ 3 in the same process is not supported
in dmesg:
pid 21560 (plugin-container), uid 1001: exited on signal 5 (core dumped)

Without plug-in browser seems to work fine.

I'm on 10-stable.
# uname -a
FreeBSD zahadum 10.1-STABLE FreeBSD 10.1-STABLE #1 r276756: Thu Jan  8 23:42:42 MSK 2015     root at zahadum:/usr/obj/usr/src/sys/BSDKERNEL  amd64
# ident /usr/ports/www/firefox/Makefile
/usr/ports/www/firefox/Makefile:
     $FreeBSD: head/www/firefox/Makefile 375599 2014-12-25 20:55:54Z bapt $

It seems the error is related to this bug:
https://bugzilla.mozilla.org/show_bug.cgi?id=1051209

Sorry if the problem has already been reported.

Thanks,
Eugene.