Mozilla and the Tor Project are in the early stages of exploring the inclusion of Tor’s private browsing features within the Firefox web browser in the form of a privileged extension. This comes on the heels of a previously expressed intention of including some Tor capabilities within the browser in a Super Private Browsing mode according to Mozilla’s public Research Grants 2019H1 report. The Tor Project and Mozilla are both researching considerations to see if integration is possible. This would not be packaged with the browser by default, but would be something that users could download from addons.mozilla.org to experience what an eventual full integration with Tor could look like.
Source: https://www.bleepingcomputer.com/news/security/mozilla-firefox-tor-mode-likely-to-start-as-a-browser-addon/