Always existed on firefox at least. It's super old feature but modern interfaces seem to have mostly dropped or ignored it. On firefox depending on the distros it would be disabled, changed, etc. It conflicts with the middle click pasting from the second buffer feature. It's like the backspace button going back, depending on the place it either works or is changed to meaning something else. At least these 2 were almost always different on firefox when using windows vs Linux and probably the first thing a user using Firefox moving from windows to linux would notice.