[Osiris]

If you want to make sure that you never miss a change on your favorite website again and stay ahead of the crowd by always knowing when the website has been updated you do need the Update Scanner Firefox extension. It basically monitors any website that you have added to it and informs you whenever a change has been made on the website. You may alter the change threshold so that you are not informed about minor changes on the website.
After installing the Update Checker extension you will see a new icon in your status bar. This icon will be gray if there are no updates and change its color if there are updates. A small balloon text will also be displayed right above the arrow.
There are two ways to add new sites that should be constantly monitored for changes. Right-click a website and select Scan Page for Update to add it to the list of monitored sites.

The second option would be to click on the icon in the status bar which opens a sidebar with all the sites that are currently monitored. If you click on New Entry in that menu you have come to the same menu.
The url and the title of the web page are filled out automatically and you only need to decide about the Change Threshold and the time between Autoscans.
The Change Threshold can be set to recognize any changes on the website as an update or only recognize them if a certain character limit has been reached. (10,50,100,500 and 1000)
The Autoscan option defines the interval in which each website is checked for updates. The lowest value is 15 minutes while the highest is once per day / manual scan.
I personally like this extension. I use it to monitor websites that I visit often to see if they updated their pages. Especially great for blogs and sites like digg or delicious.