PortableApps.com releases Private Browsing enhancement for Portable Firefox
You'll need to have Portable Firefox itself installed to use the privacy-enhanced version, though the two don't share profile data or bookmarks. It's a good way to make sure you never mix your Private and non-Private browsing sessions and it also allows you to run both browsers side-by-side. If you're looking for something with even stronger privacy features, check out the Tor browser bundle (Firefox) or OperaTor, both of which use the Tor project to anonymize your browsing.
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