How to remove tracking cookies?

You could reset safari. Safari> Reset Safari. Once you get the menu, just check all of the things you would like to wipe clean and hit reset. Works great.

In Firefox, menu Tools > Clear private data. Use the check boxes to select one, some, or all.

Best solution's not to get them in the first place. In Firefox, you can restrict cookies to sites you explicitly approve. I've been doing this for years, and it's an excellent way to stay cookie free.