As a workaround, go to Firefox menu ‣ Options ‣ Content, and click the "Advanced..." button that's next to the "Enable JavaScript" check box. A dialog will appear, in it, deselect "Disable or replace context menus".
As a workaround, go to Firefox menu ‣ Options ‣ Content, and click the "Advanced..." button that's next to the "Enable JavaScript" check box. A dialog will appear, in it, deselect "Disable or replace context menus".