Firefox collections are groups of related add-ons assembled for easier sharing.  This idea was launched from the Firefox Add-ons site several months ago.  Since some time has passed, I thought it might be interesting to check back in with this online Mozilla feature to see which collections are the most popular out there.
Here are the most popular add-on collections for the Firefox browser:

Windows 7 Theme for Firefox 3.5
32430 subscribers – This collection of add-ons were gathered to [...]

It is no secret I am a big fan of Gina Trapani’s line of “better” add-ons for Firefox, so I can tell you I was more than excited to see that they had been rolled together as an add-on collection, so you can grab them all at once. 
Which extensions make the list?
Better Gmail 2 – Add useful extra features to Gmail, like hierarchical labels, an unread message icon on your browser tab, file attachment icons, and more.

Better Amazon -  [...]

It would not make any sense to have an add-on collection without having a collector to collect them with.  Alongside the new collections feature on the Firefox Add-ons site – there is an extension to go with it.  The Mozilla Firefox Add-on Collector will help you discover and organize your favorites into easy to manage collections.
How can you access them?  Well, collections that you have marked as favorites in the Collection Dire4ctory will show up in a special [...]

Along with the new Firefox Add-ons web site, the people at Mozilla also treated us to a new feature called collections.  What are they?  Well, they are a group of related add-ons that are assembled for easy sharing. 
Here are some of my favorites I have found thus far:

Web Developer’s Toolbox 12 add-ons to help you speed up the development process when it comes to web development and managing the ins and outs [...]

Since the release of collections of add-ons for Firefox, it seems like everywhere I turn I see somebody else offering ways to bring things together (although I am sure Opera would say they did it first).  With that in mind though, I would like to introduce you to Cluster Tabs.  This add-on for Firefox will let you easily cluster web pages together for easier sharing and saving.

Creating your own tab cluster is easy to do.  Once you have installed [...]

Have you seen the new menu item on FirefoxFacts.com?  I have gone through the four years of archives I’ve posted here to find all of the “best of” Firefox-related posts.  Here is just a small sample of the posts you will find there:

Tweak up the Bookmarks Bar in Firefox
10 Popular Web Designer Tools for Firefox
Turn Your Firefox into an Arcade
10 Great Money Saving Add-ons for Firefox
7 Amazing Musical Add-ons for Firefox

Be sure to check out the new “Best of [...]

There are several add-ons for Firefox that will change the way you can interact with images and galleries, and joining that clan of extensions is OutWit Images.  It is a simple, straight to the point image browser for the browser.  It does all the catching, saving and auto-browsing for you.

The thing that makes OutWit Images different than other image browsers, is it allows user to save images right to the hard drive and browse from there.  From within Firefox, you [...]

No, before you ask this Firefox extension has nothing to do with librarians. Think of it as a collector of your favorite extensions. The Compact Library Extension Organizer takes all your extensions and themes and makes them into one single installable .xpi file.
[Learn More About CLEO!]