The headline feature for Firefox 91 is what Mozilla calls more comprehensive logic for its total cookie protection. The feature, which isolates cookies to prevent sites from using them to track users from site-to-site, first appeared in Firefox 86 in February. Firefox 91’s version claims to stop hidden data leaks while making it clearer to users what sites are doing with their information.
Moving forward, Firefox will also start using the more secure HTTPS protocol for establishing encrypted connections to websites while in private mode. Google announced earlier this year that it’s planning to add an HTTPS-first mode for Chrome as well.
