Firefox doesn't have a minimise option because it implements its own title bar. You can disable that in firefox prefs. Or the native menu is accessible with win

Firefox doesn't have a minimise option because it implements its own title bar. You can disable that in firefox prefs. Or the native menu is accessible with win key + (right?) click. I wouldn't know exactly because I've never once felt the need to minimise a window in gnome 3+. People develop and use gnome because it works well and they like it.