Here are the instructions on how to install the Greasemonkey add-on for Firefox.
1-First of all, you need the installation url:
2-Click on where it says “Add to Firefox”. Wait for the countdown to end and click install.
3-Once the installation is finished, click on “Restart Firefox”. All the tabs and work that you had before will be restored , so nothing will be lost.
4-After the restart,you should see a new window that tells you if the installation was successful or not.
5- At the far right corner at the bottom of the browser, you will also see a face of a monkey that will tell if the certain script is enabled and working at the time. An unsmiling face obviously means it is disabled. Click on it once to enable/disable
Now you are ready to go!
Video Tutorial 1 - Video Tutorial 2