Have you ever noticed that the browser's performance get slower as times goes by? One of the culprits may be the cookies. Many websites set cookies that expire in the far future, tens of years from now. As you browse the internet the amount of cookies the browser has to store grows inexorably, easily reaching the tens of thousand. Yes, even that website you visited only once, four months ago, probably has a couple of cookies laying around in your browser.
To improve performance of Google Chrome/Opera, EditThisCookie can be set to automatically reduce the expiration dates of cookies, so that all those website you visited months ago don't keep slowing your browser.