In a recent update to the Firefox Nightly release, Mozilla brings a new settings page that allows users to control from the browser’s configuration interface. To experience this new setup, you need to run the latest version of the Nightly channel. Media editors have tested firefox 79.0a1 (2020-06-23) (64 bits) and if you are also interested, click here to download it.
After opening the browser, enter “about:config” on the address bar to go to the Flag configuration page. Then, in the search bar at the top, enter “browser.preferences.trial” to find the Flag and set it to enable.