I haven't tried it yet but I think this is where it is linked...
http://www.gamesas.com/index.php?/topic/1110931-stuck-in-rivet-city/page__p__16287060__fromsearch__1entry16287060
I'd been using it since JustinOther made it...at least, I think he made that fixed esp. It wasn't hosted on Nexus, not an official release, or anything. Just something he did up in a couple of minutes for those of us with Rivet City issues.
I've always used the UF3P, but recently for my latest character have had it completely disabled. I get the same amount of crashes as if I was still using it, so I don't really know if it causes most of the problems. I haven't noticed a difference, other than the odd floating tree/bush/rock or strange bottomless pit under a pile of rubble.
I know why Quarn couldn't continue with it (well, heard from other people) and it's understandable that he hasn't been back (as far as I know) to continue working on it. I used it in Oblivion and as it was updated frequently I never had issues. Because this version is now outdated and unfinished it's bound to cause issues. Maybe not for everyone, but some people I guess.
I see FWE has dropped the UF3P support plugin. I don't really know what its purpose was, anyway. A bit over my head, I think.
Recently I read a post (by someone I always take notice of) suggesting not to use it. I'd seen him say it over and over but only now just decided to stop using it, myself. I hadn't had issues caused by it, but as it's outdated and I'm trying to make my load order smaller it was one mod that I could 'let go.'
Edit: Spelling