A firewall doesn't block people from being able to see your ip address, it blocks people from being able to .G.E.T to your ip address, meaning, there is a smaller chance that someone can hack into your computer. You can open holes in your firewall for specific purposes, and if you do, you are more likely to get hacked.
And about blocking ip addresses from a website- usually this doesn't work because many people have dynamic ip addresses ("floating"). What most websites do is block a family of ip addresses, meaning, any ip address that begins with say... 66.84.214. So that would include 66.84.214.0, 66.84.214.1, 66.84.214.2, 66.84.214.3, etc all the way up to 255 (they only go up to 255). So you can see that isn't good because then you are blocking a huge group of people, not just one person.