Firefox Beta and Developer Edition
Release Notes

Firefox has a new command line parameter, --kiosk, that opens Firefox in fullscreen mode

Windows users now have the ability to pop out videos on the web into an always-on-top video player using the Picture-in-Picture feature! For most videos, this can be accomplished by hovering the video with the mouse, and clicking on the Picture-in-Picture toggle.

Locales added: Catalan (Valencian) (ca-valencia), Tagalog (tl), Triqui (trs)

Redesigned internal configuration page (about:config)

A new Certificate Viewer that is easier to use, with more features and more detailed information.

Using the new server-timing information in DevTools' Network panel, developers can analyze the server-related timings in context of other request and response details.

Subgrid greatly enhances the utility and flexibility of grid layouts by allowing the grid of a child to use the tracks defined on the parent. In addition, the DevTools grid inspector has been improved to support subgrid.