Facebook, Google, Twitter, and all those other services that sell ads want to know as much about you as they can possibly find out. Consider for example Facebook’s Like button that is part of most web pages: even if you don’t click it, Facebook knows that you have viewed that page. How can they know? Since you have logged in to Facebook before, they have stored a cookie in your browser. And the Like button’s image is loaded from Facebook’s servers, so that cookie is sent to Facebook, together with information about the page that you’ve just visited. (My blog does not contain any tracking codes, not even Google analytics.)
So how can you avoid this? You could delete all stored cookies every single time you log out of Facebook (and Twitter and Google and…) but that’s not really convenient. Fluid is a small browser for Mac OS X (based on the same WebKit engine as Safari), but with a twist: instead of using the application to browse the Internet, you create specialized browsers for specific websites. I’ve set up a number of them: one each for my personal Facebook and Twitter accounts plus a couple more for accounts that I help maintain for my historic railway club.
Since these specialized browsers all store their cookies seperately from each other, I can use my main browser without ever having a Facebook or Twitter login. For those services, I appear as some random surfer, not connected to my actual profile.
Of course, this little trick is not perfect. WIth advanced analytics that all the ad networks employ, some information is still gathered about me (such as when I click a link in my Facebook browser that takes me to a different website), but I still feel a lot better about not giving away all my browsing history all the time.