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x adds a toolbar button from which you can quickly clear privacy sensitive data, specifically: history, form info, saved passwords, download history, cookies, and the cache (both disk and in memory cache).
Clicking the button gives you a dialogue window from which you can select which data you want clearing.
It doesn't automatically clear upon exit, you must click the button and press OK. If you decide to try it, after install and restart, right click the toolbar > customize and drag the paranoia button to the tool bar.