Go to the Update Scanner install page and click the green "Add To Firefox" button.
Click on the up-arrow icon in the status bar to open the Update Scanner sidebar.
You can also use [Alt]-U to open the sidebar.
Go to the web page you wish to monitor for updates.
Right-click anywhere in the page, and select "Scan Page for Updates...".
Select how often you would like the page to be scanned, then click the "Ok" button.
The other settings can be left at their default values.
Now whenever the web page is updated, you will see a notification popup.
The up-arrow icon in the statusbar will turn blue.
Updated web pages appear bold in the sidebar.
Click on an item in the sidebar to view the updated page.
Any changes will be highlighted in yellow.