How to disable Firefox un-maximizing window via double clicking the tab toolbar?

Double clicking the tab toolbar (or any other toolbars) results in Firefox widow being restored (un-maximized). This is driving a lot of people nuts because they accidentally double click the toolbars. My own mouse has to be replaced because it's bugging out double-clicking for single clicks.

How do we disable Firefox from changing the window size when the toolbars are double-clicked?

The simplest workaround.

Open Firefox. Click ☰ → More Tools → Customize Toolbar. Check Title Bar in the lower-left corner. Click Done.

With a separate title bar enabled, double-clicking the tabs no longer restores the window because the tabs are no longer acting as the window's title bar.