Clearing cookies will remove all stored customization that you have made on a website. An example are the Google preferences on the [http://www.google.com/preferences?hl=en Google Search settings] page. Also the choice to let a website remember you and log you in automatically with each visit is saved in a cookie. You can also try to clear the History, because a large history also can cause a slow response (Firefox needs to check the history if you click a link). See also [[Clear Recent History]]