I stumbled upon this upon reading a slashdot comment, yeah, where else?
So I'm sharing this because it really improves the speed, specially on a notebook which struggles to keep up to speed with all that AJAX crap (pun intended?).
So the addon you would want to install is called BlockSite and can be found exactly here on the Mozilla addons site
Once installed configure your BlockSite preferences to include:
$ cat list
You can also create a file out of that cat output and use BlockSite's import option
Here's to a better browsing experience