I am looking for something for linux/gnome along the lines of Malwarebytes' ip blocker. Basically use a blacklist and block http requests if one of those ips/domains are called. I know Firefox blacklists but I know on my Windows 7 machine that the Malwarebytes' ip blocker caught a lot of things that Firefox's didn't.
You might like Moblock:
With a Gui:
You can add all kinds of lists from iblocklist.com, and create your own.
Hope that helps.
Uncomplicated FireWall (UFW) is ubuntu's equivalent tool.