One of the most often requested features in the private browsing support for Firefox has been the ability to open a private window without needing to close the entire session. Over the past 19 months, we have been working on […] to make it possible to open a private window without needing to close down the entire non-private session, and today, I’m happy to announce that we now have the first experimental builds with this feature ready for testing.
[Per-window private browsing ready for testing now! sur Ehsanakhgari.org]

Feature disponible depuis longtemps sous Chrome. C’est d’ailleurs ça qui m’a fait switcher définitivement.