The website does not allow right click. I have tried to uncheck "Disable or replace context menus"� in the Firefox but still could not disable "Do not right click."� Do you know how to disable it?

Try this: Re-enable Right-Click When Web Pages Disable it (http://www.lifehack.org/articles/lifehack/re-enable-right-click-when-web-pages-disable-it.html)

Or this: http://userscripts.org/scripts/show/30096