Starting with Firefox 91, users will be able to erase browser history for all visited websites. The new feature, dubbed Enhanced Cookie Clearing, helps you delete all cookies and supercookies stored on your computer by websites or web trackers. Mozilla also announced that private browsing windows will automatically switch to secure HTTPS connections by default. By upgrading all connections to HTTPS, Mozilla aims to protect users from man-in-the-middle (MITM) attacks trying to snoop on or alter data exchanged with web servers.
Source: https://www.bleepingcomputer.com/news/security/firefox-adds-enhanced-cookie-clearing-https-by-default-in-private-browsing/