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Still, if you're feeling adventurous, you can try the latest Firefox 3.1 build which finally has this feature. It's simple - although not as elegant as in Chrome, which doesn't require closing your current browsing session - choose "Private browsing" from the "Tools" menu; your current session will be closed and saved, and a new, private one, will open. This new session will leave absolutely no trace of your online activities; once you're finished, uncheck "Private browsing" and your previous browsing session will be restored.
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