GMail Manager is the best. Unfortunately the original author stopped doing regular updates on it but someone forked it and is trying to keep it up to date. You can get it here:
https://addons.mozilla.org/en-US/firefox/addon/gmail-manager-ng/
Works perfectly for me.
Er... that's built in to Firefox. Click the Middle Mouse Button and then you'll see a round icon with arrows in it. Just move your mouse down and it'll start scrolling. The further you move the mouse down the faster the scroll speed.
Ah cool for GMail Manager, I'll try it out.
And yeah I know about the auto scrolling (that's actually built-in into windows and works in pretty much any applications...unless it's a logitech thing...anyway).
It's not really what I'm looking for. What's cool about the addon in Chrome is that I can enable the NeoGaf Live thread addon so that one of my tab will automaticaly refresh every minute and then activate the Auto-Scroll addon and, everytime the tab refresh, it will slowly scroll down to the bottom of the page. It's great for when I'm playing a game on the main screen but still want to follow a thread in the second screen.