Wrong advice: it works on PPC. Rated 4 out of 5 stars
This addon works for me. Early indications are that it has a useful set of options.
The advice on http://support.mozilla.com/en-US/kb/Opening%20PDF%20files%20within%20Firefox?s=pdf&as=s (Opening PDF files within Firefox) seems to be wrong. "Firefox PDF Plugin extension" works for me on a PPC with OS 10.4.11 and Firefox 3.6.19. The Schubert plugin, however, doesn't work for me at all, does not appear in Firefox's plugin list, and is not available as an option under Firefox-->Preferences-->Applications for .pdf files.