The latest nightly builds of Mozilla Firefox include a new feature that significantly improves the speed of the Back and Forward buttons. When using Back and Forward in older builds, the page is retrieved from the local cache rather than the Internet but Gecko still has to reparse the HTML and use it to rerender the page, which can take a while with more complex documents. With this new feature, the rendered page is kept in memory, which makes Back and Forward performance much faster (almost instantaneous). In addition, going back or forward to a page cached in this way shows the page exactly how it was when you left it, in compliance with section 13.13 of RFC 2616.