Mozilla’s Firefox is the most popular browser online (by choice – default Internet Explorer installations don’t count), and for good reasons: it’s stable, relatively fast and has an amazing collection of useful add-ons that can extend its functionality by a very high degree.

The developers community is also growing bigger every day, and the new 4.0 release that is still in development promises to be the fastest and most functional Firefox yet (currently, Chrome is the fastest browser around, thanks to it using the newest Javascript and page rendering engines).

Firefox is available for all desktop operating systems and there are plans to bring it to mobile devices like the iPhone, Android phones and MIDs, Palms and others. As a matter of fact, Nokia’s N900 (that runs on Maemo, another open source OS based on Linux) has already got a working and relatively stable Firefox release.

Of course, Mac OS X is no exception – Mozilla actively develops and maintains Firefox for Mac, and the updates are released at the same time as those for the Windows version (unlike the Linux version, which has to wait days, weeks and even months to get the latest update).

Safari is a great browser, but it certainly doesn’t have the power, flexibility and security of Firefox, and those are all very good reasons to switch. Besides, if you do any web development and design on your Mac, you’ll certainly want to have a copy installed to test your work.

So, here are some of the best add-ons that can definitely improve your Firefox on Mac experience (especially for developers):

NoScript. This add-on is one of the most important reasons why Firefox is so popular. NoScript is an amazing security add-on, which can virtually eliminate any security threats that may be present on various web sites. It works by disabling Javascript and XSS scripts on all sites, except those that you know are secure (Google, Youtube, Facebook and other sites you use frequently). No other browser has support for this kind of functionality, do if you want it, Firefox is the only way to go.

AdBlock Plus. Adblock goes hand in hand with NoScript. This add-on lets you block Flash components and ads on all sites except those that you like and know are secure. Using it together with Noscript not only gives you a break from all the ads and banners, but also makes your web surfing 99% safe (only some exotic and highly complex attacks can work if these 2 add-ons are active).

FoxTab. If you like Safari’s Top Sites feature, you’ll be happy to know that Firefox has it too, and it’s also much better! FoxTab allows you to have a custom Top Sites list, switch between tabs and view recently closed tabs in a very beautiful 3D interface, which is also customizable (backgrounds and type of 3D animations). It’s a great add-on that will certainly improve your browsing experience.

Greasemonkey. Greasemonkey scripts have gained quite a large following in the past 2 years. And that’s all thanks to their amazing ability to change the way any web site or page is displayed, by intercepting and modifying the code before it’s rendered and displayed on the screen. Despite how it sounds, it is actually completely safe, as all the changes are performed on the user’s end, without sending information anywhere. If you don’t like the way any web site looks (even Facebook and MySpace) and think you can make it look better, you will definitely benefit from the Firefox Greasemonkey add-on.

Ubiquity. Ubiquity is a lot like Greasemonkey above, only it is targeted towards executing complex scripts and actions by using normal language commands. For example, you could easily have Ubiquity go to Google maps, find San Fracisco, take a screenshot of the map and insert it into your email, all by typing “Insert map of SF” when writing an email in Gmail or other online email client. It can also modify web pages, but Greasemonkey is much more suited for that, plus there are tons of already pre-written scripts there, unlike in the Ubiquity database.

Read It Later. This is a very useful add-on that lets you save pages for later viewing with the click of a button. You can save them online using a RIL account or offline on your computer (yes, you can view them anywhere, even without an Internet connection). Great if you have to go somewhere remote and want to have access to all of your unread RSS feeds or useful online pages.

There are a lot of other great add-ons in the database, just do a search. The best add-ons that are available for Windows are also most probably already ported to the Mac OS version of Firefox, so if you read about other useful Firefox add-ons on a website, be sure to check out if there’s a Mac version out there.