AutoPager is a useful firefox extension which allows you to automatically loads the next page of any website inline when you reach the end of the current page for infinite scrolling of content. For Example like google search results provide a navigation links to next 10 pages from the first page of google search result, this extension can allow you load all these pages automatically yourself to click on these links to navigate.
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This extension works with a ton of sites, including Lifehacker, the New York Times, Digg, and Google etc. You can add your own custom auto paging to unsupported sites, the site wizard feature makes it easy for auto discovery the links and content on a site. It also includes a adblock similar features to allow you filter out the ads from the contents in the loaded in webpage and It works well with most of the grease monkey scripts.
Note: It works with Firefox: 1.5 – 3.7a1pre