Rated 4 out of 5 stars
I just noticed that the old PDF Browser Plugin from SchubertIT (http://www.schubert-it.com/pluginpdf/) will work in FF 4.0.1. The browser has to be launched in 32-bit mode, though. It's better than nothing, although I like the Google PDF Plugin much more than the SchubertIT thing. Both plugins seem to be abandoned, unfortunately. I really don't understand why FF on MacOS X still lacks a decent PDF Plugin that is being developed further. HTH!