The state of PDF support in Firefox on OS X has me stuck at FF 3.6, and it doesn't look like that'll be changing for a while (unless I want to experiment with random xpi's and running FF 4+ in 32-bit mode, etc). Until that's resolved, all the fancy CSS tweaks in the world won't mean a hoot.
On OS X, there's possibly the best PDF viewer ever, in Preview. I'm curious why you'd want so strongly to avoid using it?
It's much faster than the bloated beast that is Acrobat, but I'd say about 20% of the documents I open in Preview have to be viewed in Acrobat to be usable, so I've just defaulted to avoiding Preview instead.
A good, fast PDF viewer in the browser would be far better than either of those options.