What is the most frequently used type of navigation on a website? Links? Images? Drop-down menus? Wrong. It’s the browser’s back button. And buried in the developers’ explanation of Firefox’s so-called “memory leak” is this little nugget of statistical goodness that (er) backs me up: “To improve performance when navigating (studies show that 39% of all page navigations are renavigations to pages visited less than 10 pages ago, usually using the back button), Firefox 1.5 implements a Back-Forward cache that retains the rendered document for the last five session history entries for each tab.” The full explanation is on the Inside Firefox site.