The idea of having a Firefox extension that gives you content related to what you are looking at is nothing new really, however I have found a Firefox add-on that will help you get it done in a new and exciting way. 
Headup underlines words on pages when you browser.  When you hover over those words, you get relevant content from popular web services. 

Technically speaking, they  “presents you with textual and rich media content related to the [...]

Want another way to find out what other people are looking at?  The Fast Forward add-on for Firefox is an interesting one.  It adds a fast forward button to the browser, so you can see what is the top page that most people look at after looking at the page you are on.  For example, if you were on FirefoxFacts.com, and hit the button – it might lead you to Mitchelaneous.com, because more people went to that web site [...]

So what type of questions would you have for the mind behind NoScript?  I recently got to chat with Giorgio Maone, the creator of possibly the most popular security related extension for Firefox.
Why would the random Firefox user off the street be using NoScript?
Firefox is an extremely safe browser, because it can take advantage of an open and agile development process, a very security-minded core development team and a multi-vendor security coordination group, including people from major Linux distributions [...]

Wish to access only the images on a page and none of the clutter – like those annoying big words, style and layout? For those out there who want the images and the images only the Browse Images add-on should get the job done.
Once installed you can browse all linked images of a page one after another or all at once.

On the positive side of things, Browse Images does make it rather easy to browse through multiple images when [...]

Want to view, edit, publish video for the Web without worrying about having the right plugin, or doing the right version for the right people depending on the video method they like the most?
Well both Mozilla and the Opera people are getting behind a movement to do just that.
Looks like the solution will be to use some open source technology mixed with a new tag to make embedding video in web pages easier.
Opera and Mozilla officials say the changes to [...]

When web development and design is mentioned, everybody’s top Firefox extension is the Web Developer toolbar. There are a few other choices out there for design and coding tools that you might have not of seen before.
View Source Chart – This extension does one job and does it well. It draws colored boxes around different source codes to help you read the information better. Instead of black and white confusing stuff – it’s all colored man. [...]

What, you didn’t know that Firefox had more than a few branches off from it’s Mozilla base? To keep things simple, we can think of them as cousins (just hope they don’t start kissing). Both the Webrunner and Instantbird projects show a lot of promise and might just be the next big thing for the Mozilla team.
Webrunner – WebRunner is based on a concept called Site Specific Browsers (SSB). The idea behind Webrunner is to make a [...]

Not every web site does that best job when it comes to giving you a printer friendly version of the web page. Lets say for example, you want to print out a story on CNN.com about the war in Iraq or your favorite celebrity.
Now you could just print the page that is there, but that is going to give you all the ads, logos and other junk you don’t want on your paper. The Lexmark crew [...]

Finding yourself in a bind with your web site design? Maybe you just can’t get your CSS to level out with your HTML? If you find yourself in these shoes we talk about, you might need to pick up the Total Validator extension for Firefox.
Perform multiple validations and take screen shots in one go. This 5-in-1 validator works with external, internal, or local web pages using the Total Validator service or local copy of the Pro desktop [...]

Unlike most parental software you can put on your PC, I think Glubble might stand a chance to really do some good. Glubble is an attempt at making a kid friendly version of the Firefox browser. To get it up and running, all you need to do is to install an extension. Its just that simple
Glubble Trusted Surfing for children under 12 years of age enables families to be sure they only see the best of the [...]