Wow. OpenOffice 2.0 provides a Firefox plug-in - and it's damned fast even on my hunk-of-junk laptop.
I'm pretty impressed - at work we pump out PDFs through an open office machine and a python bridge; but this would make our document rendering much much faster :)
If you've already got OpenOffice 2.0 on your machine, look under the Tools -> Internet menu and start seeing how it performs on files in the wild.
Hell: OOo + ebooks, anyone?