Most major websites track their visitors' behavior and then sell or provide that information to other companies (like advertisers).
Have you seen, that when you surf on FB into the frame on top right, you receive more suggested site, in relation of your product search in other sites?
This features is called "personalization", it's legal after you accept to use yours FB credential to login in.
Good, do you remeber "Netiquette" (if not read associated link), now FireFox introduce a new features
"Do Not Track"
Firefox has a Do Not Track feature that lets you tell websites you don't want your browsing behavior tracked. This article explains what tracking is, how the Do Not Track feature works and how to turn it on.
When you turn on the Do Not Track feature, Firefox tells every website you visit (as well as their advertisers and other content providers) that you don't want your browsing behavior tracked. Honoring this setting is voluntary — individual websites are not required to respect it. Websites that do honor this setting should automatically stop tracking your behavior without any further action from you.
Turning on Do Not Track will not affect your ability to log in to websites nor cause Firefox to forget your private information — such as the contents of shopping carts, location information or login information.
- At the top of the Firefox window, click on the button and then select.
- Select the panel.
- Choose Tell sites that I do not want to be tracked.
to close the Options window