The best explanation of private browsing comes from this paper:
"Unwanted information from the user’s browsing history will not appear in the history bar, auto-filled forms, or search suggestions. Private modes thus help users hide browsing sessions from people sharing a device with them"
Private Browsing does not 100% prevent
Tracking by websites you visit
Many people have a false understanding that private browsing will magically protect you from advertisers and spyware . Firefox does allow blocking while in private mode, but these are two different features .
Google chrome will still track you when using incognito mode .