There are thousands of useful (and some not-so-useful) Firefox add-ons. Finding the ones that can be useful for you isn't always easy. I've written about a dozen or so add-ons on this blog, but I've only scratched the surface of what is available. Recently, Mozilla remodeled their Add-ons page to allow for better browsing and searching. When you visit the new Add-ons page you will notice that they now feature recommended add-ons from five popular add-on categories. Another change is addition of a new featured collections category where you can access a collection of Firefox add-ons that complement each other.
Not two minutes after I published this post, Mashable ran a similar post containing the video that I've now embedded below.
Watch the video embedded below for an overview of Firefox Add-ons Collections.
Here are some of the Firefox Add-ons that have been featured here in the past:
Quick Translation - Dictionary and Translation Firefox Add-on
Lizzer - A Handy Tool for Student Blogging
Googlepedia - Wikipedia and Google Side by Side
Quietube - No Nonsense YouTube Viewing