one-site browser

Here's a good trick not many know about, I suspect. If you want to surf a site, but you want to make sure that cookies, logins, and personal data do not spread to other sites (For example Google forces you to be logged in with the same login on all their billion sites, youtube, blogger, etc.). Then you can use an app like Fluid to make a one-site browser. It's simple an isolated browsing app which you use for only one site. (Can be for security too, like your bank or Paypal.) Fluid is for Mac, but I'm sure windows has similar apps.