How to Make Your Own Firefox Addon

Stefan Neagu 18-01-2010

<firstimage=”//” />fflogoIf you want to start coding, there’s no better way than with Firefox add-ons. If you’re familiar with standard web programming languages, you’ll be up and running in no time. If you’re not, learning a bit of web tech won’t be very difficult, and learning how to make your own Firefox addon will surely prove valuable, as more and more things move to the “cloud”. Even more, thanks to Firefox’s ever increasing market share, you will be potentially influencing the browsing experience of millions of people; certainly a enticing perspective.


Firefox was designed to be a very minimalistic browser, which is a good thing. This way, each user can choose which extra features he wants to install. While it may inconvenience some users who, quite frankly, are downright lazy, the extensibility of Firefox reduces inherent software bloat and improves performance.

make your own firefox addon

Anyone can develop an extension for Firefox, without any fees or approval procedures. While some conditions have to be met in order to make your own Firefox addon and have it appear in Mozilla’s online repository, you can host your own extension and users will be able to install it. Having your extension included in the official repository gives you more exposure, as most users will simply follow the link in the Add-ons Manager and not directly search Google.

A recent pilot program allows for self-hosted extensions in the repository search results, but they are marked as not verified my Mozilla. Add-ons that go to the AMO verification get a certificate which will trigger the Add-ons Manager on the user’s system to display a message that the extension was verified and comes from a trusted source.

make your own firefox addon


Extensions can use these types of technologies: CSS (Cascading Style Sheets), JavaScript, DOM (Document Object Model), XPCOM (Cross-Platform Component Object Model), XPConnect, XPI (a cross-platform installer module), XUL (an interface to the XML – Extended Markup Language).

Your extension can add features, such as RSS readers, toolbars, bookmark organisers and FTP clients. You can also modify how pages are loaded; for example, a popular add-on called AdBlock Plus How To Block Annoying Ads in Firefox Read More will remove advertisements from pages you visit. Another notable extension, Greasemonkey, will allow users to load the equivalent of “user style sheets” targeting the behaviour of web pages “on the fly”.

how to make your own firefox addon

The Mozilla Foundation provides a website for developers, which contains a wealth of information about how to make your own Firefox addons – without registering or paying a fee. There you can learn all about the APIs, languages and even case studies that cover the development from start to finish. If you’re stuck, you can go ask for some help on the forums.


You should start with Firefox Add-ons Developer Guide, which was written by Hideyuki Emura, one of the first developers on the Firefox platform. It explains the thinking behind Firefox’s modular design, the different types of functionality an extension can have, all about the layers of technology that need to be combined in order to make extensions easy to sue while powerful. With its characteristic “no-nonsense” approach, you will be able to learn the basics of coding extensions in no time. Another good tutorial was written by Robert Nyman,  which covers the development process from top to bottom.

You might also want to subscribe to the Mozilla development blog, which keeps you posted about the latest updates to the repository, workshops & events,  and more.

Do you have any developing experience you’d like to share with our readers? Voice them in the comments.

Related topics: Mozilla Firefox, Web Development.

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  1. Tom Doodins
    May 12, 2015 at 1:11 am

    What's JetPack?

  2. geeknik
    January 19, 2010 at 4:57 pm

    You should have posted a how to on making a Jetpack for Firefox instead. Extensions are fast becoming obsolete and Mozilla is going to be pushing Jetpack development instead. :)

    • asdfghjkl28845
      April 29, 2015 at 10:13 pm

      And yet, five years later, addons are still very much more popular.

      • Tech Man
        February 19, 2018 at 4:06 pm

        By Now, 8