In Firefox, I use this:
http://www.schubert-it.com/pluginpdf/
It's a very light-weight, simple, quick plugin for PDFs. It also is nice in that it has a button up top to launch the PDF that's in-browser in Preview, Adobe, or whatever else you have installed (that's registered to open PDFs).
I actually also generally use it in Safari. This feature is the primary reason why.
A few minuses:
- It's fast in large part because it does no quartz smoothing.
- It doesn't have lots of the features that Adobe's reader does, but then I've never installed Adobe's reader in four years on Macs, and it doesn't have the annoying update behavior, etc.
- It doesn't seem to respect scrollwheel.
- IIRC, it doesn't have in-document searching.
Basically if I am serious about the PDF, I hit the diamond icon and launch it in Preview (You can also then easily rename the copy that's already in the cache and move it to another folder).