I can not tell you too many particulars, but a friend of mine did get FF installed and working using the files from the synology wiki and the more up to date FF shown in the forum, what I gleaned from him was starting with a clean firmware install,
He unTarred all of the files from the wiki (gdbm,Libid3tag, sqlite) from the root directory.
Then he unTarred the FF from the forum from the root.
He then did the the library path thing to /root/.profile from the wiki.
However, he learned that some of the libs did not exist there they wer in a sub dir and needed to be moved, you’ll have to find out which ones since I don’t know…
He could then start FF and it worked… (I think). I am trying to get him to do a writeup of what he did so that I can post 🙂 Hope this can start you down a path to this working, because FF rocks!
Craig