Greasemonkey (firefox addons)

Greasemonkey is a firefox addon which allows the user to install scripts which are loaded automatically as the web page loads in the browser. They are site specific means they work only for that site and not any other. Gresemonkey is very useful to add your own function to the web page to make your work easier and faster. it can be used for auto filling forms, to change the view of the web page, add hyperlinks or multimedia  to the web page and make your experience on the site more enjoyable.There are wide range of useful scripts which are easily available.

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To automatically find grease monkey scripts you can use another firefox addon  GREASEFIRE       Download

NOTE :- Please use the scripts from reliable source many malicious scripts can cause harm and affect your security.