Update Scanner is an add-on for Firefox that automatically check for web page updates. It is useful for staying up to date with websites that do not provide any RSS or Atom feeds.
How to use:
Install the addon.
Click on the Up arrow in your statusbar:
Select Scan Page for Updates…
Set the settings according to your wish.
Now it will check for updates in the webpage within the interval of time you have set and if any change is noticed then it will display the following message: