I was waiting for someone to develop an in-line PDF plugin for Firefox on Mac OS X, and finally it's here:

http://code.google.com/p/firefox-mac-pdf/

A while back there was an older plugin that only worked on PPC Macs on older Firefox versions, but this one is designed for Firefox 3, and works great on my Macbook Pro. It doesn't have a lot of bells and whistles, but it gets the job done.

It's been out for a couple months now, but I figured I'd post here in case someone hadn't stumbled on it yet.