Web browsers remember web pages visited by user to show visited links in purple and not visited links with blue color and for auto-completion in the URL bar.  Some websites do track user’s browsing history based on the loophole in browser such as this called as history Sniffing.

History sniffing is fixed in upcoming  Firefox 4 final, however here is how you can disable history sniffing in Firefox 3.5 and above.

1.Type about:config in the browser.

2. Opposite to Filter type layout.css.visited_links_enabled, double click it to set its value to false.

disable history sniffing in Firefox

But with this, websites no longer determines which links you clicked neither you and you’ll not able to identify the difference between visited and not visited links.