yes, the appended terms by users is not binding. the EULA supercedes anything the authors might stick on their filters submitted to the library. if they dont submit them, then they can make all the terms and provisions they wish, but when submitted they have to agree each time they submit, so every filter in the library is covered by FF's EULA, not any author's. they, the authors may want it to be their way, but that doesnt make it so legally. so, dont worry; if it's in the library, you are only bound by the FF EULA and not what the author wishes (unless, of course, you want to be).
If wishes were horses... there'd be a whole lot of horse crap to clean up!
Craig