Ok Javascript injection is a very useful tool for hackers and all kinds of people allowing you to edit cookies view cookies a page is setting and lots of other things.
Viewing Page Cookies:
Code:
javascript:alert('Set Cookies:\n\n' + document.cookie) This can be used if you want to see the name of a cookie.
Editing Cookies:
Code:
javascript:void(document.cookie="Cookiename=Cookievalue")
This is used for editing a pre-set cookie or adding a new cookie to the list.