I asked myself the same question. I just learned about this new feature. It is called Glue.
I am taking from LiteraryEscapism's blog.
Laura with Glue explains it so well that I will just copy what she says
Glue is a Firefox add-on that connects you to friends around the web. As you visit everyday topics, such as books, music, and movies on popular sites, Glue appears automatically to show you friends who looked at the same thing, if they liked it, and even their opinion.
Everyone has their favorite book site, but this isn’t a problem for Glue. If both Jackie and I were interested in Angel’s Blood, and she visited the book on Amazon.com, and I looked at it on Barnes and Nobles we are still connected. Glue pulls people together across these diverse websites and pages to connect them around the common thing: an interest in the same book.
You might be confused reading this, but as Wired has said, “using [Glue] is actually much simpler than describing what it does.” Wired also said the Glue is “the single most useful social networking tool I’ve encountered” :) So let me show you what I mean.
Glue appears automatically at the top of the page to show other friends who have interacted with the same book around the web. With a single click you can let your friends know that you like the book. You can even leave a short “2Cent” comment which will appear whenever a friend looks at that book, no matter what site they are on.
Instantly I am able to see that Jackie likes this book. It’s worth pointing out again that Jackie appears on this Barnes and Nobles page even though she visited the book on Amazon. It also shows other friends who looked at the book, along with other interesting people. When I scroll over Jackie’s avatar, I can see her “2Cent” comment, which is a link to her blog post. This is extremely useful to book bloggers since their reviews can be available anytime anyone visits that book, on any site!
By clicking on your friends’ profiles you can also see what other books they enjoy. This is all without navigating away from the page you are on.
A concern might be, “What if I’m looking at items I don’t want friends to see?” For example, if you are shopping for a gift. All you have to do is scroll over your picture, and delete that book from your history.
You can watch a short video on http://getglue.com/ to get a better understanding of Glue.
The web is filled with noise, and Glue is able to pull relevant information exactly when and where you need it.
For questions about Glue please email us or Twitter: @adaptiveblue.
You might be wondering why I just posted about Glue. Well here comes the ah ha moment. Literary Escapism is hosting a contest. One of the ways to enter is to post about Glue. For more details check it out here