Every browser lets you cover your tracks -- an essential security step when you're working on a shared computer or one where others may peek inside (think office system) -- but Firefox's privacy retention command is the simplest to call.
Press the Ctrl-Shift-Del key combination -- or if you're more comfortable with the mouse, select Tools|Clear Private Data -- and a dialog box pops up offering to delete everything from the browsing history to saved passwords. (By unchecking the "Ask me before clearing private data" box, you'll save yourself a second click in the dialog.)
The feature, which debuted in Firefox 1.5, can be extended with the very small extension Clear Private Data; it adds a "clear data" item to the right-click menu within Firefox, and an optional icon that can be dragged and dropped to the browser's toolbar.
