How to hide system title bar for Mozilla Firefox

Some Firefox installations, such as in Ubuntu, automatically display the system title bar. It is redundant with the tab bar title and wastes precious screen real estate.

The system's title bar can easily be hidden for Mozilla Firefox from its Customize panel.

1. Open Firefox menu by clicking on the hamburger menu icon on the top right of the window.
2. Click on the Customize menu.
3. Uncheck the Title Bar checkbox on the bottom left of the window.
4. System title bar should no longer be displayed.