A fire button which you click and it deletes all cookies, cache, and search history.
This is similar to the existing feature in the DuckDuckGo browser, and when I used DDG (before the microsoft revelations) I loved this feature!
If added, they could also add a fireproof feature like DDG in which you fireproof websites that you log-in to so that their cookies aren't lost.
This could be an optional feature as I don't see everyone wanting it, so you could activate/deactivate it in settings, but it would be very useful imo.