This has been asked before here, but it seems currently there is no solution: Firefox's default behavior when using the mouse middle-click on an empty area of the tab bar area will create a new tab; I don't want this behavior. How can I disable it? On the posts I found here, they mention using UserChrome.css, I enabled it and tried, doesn't work. custom styles are enabled but not disabling this feature. I use DisplayFusion on my multi-monitor setup since years, and middle-clicking a window title bar or Chrome tab bar or Firefox tab bar will move the current window to a second monitor. Currently with Firefox, middle-clicking the tab bar will move the window to the second monitor AND open a new tab. I use it a lot with YouTube, so when I move a playing video to the second monitor, I get an empty tab with audio in the background. I recently moved from Chrome to Firefox, but this is driving me crazy.