Installing Greasemonkey Firefox Extension
Open Firefox add-on website and search for Greasemonkey extension or open following URL in browser.
Click on the “Add to Firefox” button.. If Firefox ask that it prevented the site from installing software. Click Edit options… to open the “Allowed Sites” dialog, then click Allow to add the Greasemonkey site to your list of sites that are allowed to install software. Click OK to close the “Allowed Sites” dialog. then again click on the “Add to Firefox”.
Now an Firefox install dialog should pop up to confirm that you really want to install. Just wait countdown to finish then click Install now button.