Firefox: double-click on titlebar maximize window instead on open new tab Recently, I noted that Firefox started to behave differently when I double-click on its title-bar / tab-bar.

It maximizes the windows as if I clicked on the semaphore + button, instead of opening a new tab like it used to do before.

Anyone knows how to get the old behavior back?
Double-click to maximise is a System pref

 menu > System Preferences > Dock

Uncheck "Double-click a window's title bar to…zoom"