This add-on adds a new menu item at the context menu (menu appeared at right click) for doing a hard refresh (CTRL+F5) of the web page. This is useful when you're developing a website and sometimes need to do a hard refresh to prevent retrieving the content from cache. Of course you can press ctrl+f5 but sometimes clicking can be convenient. Also, there's a "reload" menu item anyway so why not "hard refresh" too? ;)
From version 1.2, a button can be added by going to Firefox>Options>Toolbar layout and drag the icon to where you want it.