
Apps are hip and happenin' these days, especially with the iPhone and the iPad making waves on their respective markets. Apps have been very influential and game-changing, to say the least, that even Web giant Google is nonchalantly following in Apple's footsteps.
Unbeknownst to many netizens, however, Mozilla has its own repository of add-ons for its popular Web browser Firefox. They're not called "apps" per se, but they add a whole new dimension of usefulness to your browser.
We've taken the liberty to scour through the thousands of independently and collectively built software to give you what we reckon are the 10 most useful Firefox add-ons.

If you're going to get just one from this list, make it this one. WebMail Notifier is an email consolidator that alerts you whenever you receive new mail from your numerous accounts. In previous years, this free service was limited to Yahoo! Mail and Gmail, but it has been upgraded recently to accommodate Hotmail and POP3 servers.
Downloads to date: 3,913,137

2. Screengrab
Print Screen is so 1990s, that's why you have to up your game especially when you're capturing websites. Screengrab allows you to take snapshots of whole Web pages and to save them in a variety of picture formats. No more tedious cutting and pasting here!
Downloads to date: 3,390,143

Persona is a new feature in Firefox 3.6, and Personas Plus is just the add-on to help you personalize the heck out of your browser. This add-on is a collection of over 60,000 themes/wallpapers/skins (call it whichever way you like) that are guaranteed to make Firefox look even foxier.
Downloads to date: 21,094,957

4. Adblock Plus
As its name suggests, this free software gives you some well-deserved peace of mind whenever you're surfing the Web. AdBlock Plus filters ads, photos, malware, plus a bunch of other potentially harmful junk on the Internet that are out to take down your precious PC. Nearly 81 million Firefox users have downloaded it, making it one of the most popular add-ons ever.
Downloads to date: 80,963,329

5. Easy YouTube Video Downloader
Note: Downloading YouTube clips is illegal
Note 2: You don't care
Now that we got those 2 out of the way, it's enough that we say that Easy YouTube Video Downloader is, in fact, an easy way to download YouTube videos. It may not be as easy as using 3ouTube, but it is more versatile and it lets you download videos in full 1080p HD or even in MP3 format (audio only, obviously).
Downloads to date: 3,721,016
More unbelievably useful Firefox add-ons on page 2