One of my favorite things about the Amazon site is the “customers who bought this item also bought…” category. It shows what other people bought in addition to the product you’re looking at, and is a great indicator of the great related items out there.

Using the new Fast Forward button Firefox extension, that same great functionality can be used all over Firefox. With the click of a button, you can see where others went next from the page you’re currently on.

To test it out, I started on a New York Times article about Niger. I then was taken to several other NYT pages, before going to a YouTube video about a similar topic. It was a bit roundabout at times, and some of the choices were totally unrelated, but it was mostly stuff of interest to me. Using others’ history as a recommendation engine is a smart feature, and FF does it fairly well.

The uses for this are many: if you’re on YouTube, and want to see the video that most people went and viewed after the one you’re currently loving, Fast Forward can help you find your next favorite video. On Flickr, let Fast Forward take you through popular images, based on the one you’re looking at.

Fast Forward has the potential to be a really useful service, a bare-bones recommendation engine based on what’s currently in front of you. It is, as TechCrunch called it, “StumbleUpon with a train of thought.”

Fast Forward is a lightweight Firefox add-on, showing nothing more than a green button, right next to the back/forward buttons in Firefox. There’s no registration needed to use it either, which is key: the install is easy and clean, and starting with FF is impulse-ready.

Fast Forward’s recommendation list is growing- over 40,000 sites with over 200,000 contributions, according to their website. For some sites, though, it won’t have a recommendation for where to go next- you’ll see a grey box in your toolbar.

I like this as a potential learning tool, stumbling through topic-specific pages all over the Web, based on what you were initially interested in.