I actually came across that site earlier, but the link on the site led nowhere. Not sure if it's an old plugin or what. As for the first, I tried that on your advice. I'll play around with that more to see how it works, but on first and second attempt it only seems to make the image seem more "blurred" as opposed to "pixelated".
After I posted this question I had the "bright idea" to see if there was an app for this sort of thing. I found something that works great, for my purposes. It's a bit of a roundabout way of getting the job done -- emailing myself the portion of the image so I can pixelate it on my iPad, email it back to me to lay over top of the rest of the image in Fireworks -- but it works. And I now have a pretty cool app for messing with images.
Thanks again! I'd still be interested in an actual Fireworks extension for this.