A native Songbird port is a lot of work. I've had a deep look into it and have spend some weekends on it just to have a plan on how to actually do it. The biggest problem with Songbird is that they live in their own world. They take libraries and modify them with some random patches and at the end build everything and use it as dependencies so that you actually can build Songbird with them.
So for a native port you have to first make all of their dependencies compile fine on FreeBSD which is a lot of work on its own as it includes things like xulrunner, gstreamer and some codecs. Then you can start with the actual porting of Songbird which is a lot of code too.
To get me right. It is not impossible but you will need an huge amount of time to get it done. If someone is interested in doing it I could offer a few patches and a rough port just to get you started and plan to continue work on this later this year.