Install the prerequisites noted in the README file if you’re building swfdec and swfdec-mozilla from scratch. I found I only needed to install liboil-devel and gstreamer-plugins-base-devel in order for it to build without complaint. When installing from binary on my 64-bit os, I found I was missing a lot of 32-bit packages needed by the plugin, so my dependencies needed by swfdec-mozilla.i386 rpm was long.