Firefox Extension Course

Firefox browser is here to stay. Although fighting against Google Chrome / Chromium and Edge is a difficult task, it is still the best broswer in the world. Firefox allows diversity which no other browser enables. Learn how to create Firefox extension, the old way and the new way, using the MDN. Firefox extensions can create a whole new look and feel to the browser and transform it to something totally different. Firefox ectension development will teach you how to create new extension for Firefox using the XUL, JasvsScript, HTML5 and CSS.

Using Add-ons

What is an add-on?
Add-ons are small pieces of software that add new features or functionality to your installation of Firefox. Add-ons can augment Firefox with new features, foreign language dictionaries, or change its visual appearance. Through add-ons, you can customize Firefox to meet your needs and tastes. Learn more about customization
Will add-ons work with my web browser or application?
Add-ons listed in this gallery only work with Mozilla-based applications, such as Firefox, Firefox for Android, SeaMonkey, and Thunderbird. However, not all add-ons work with each of those applications or every version of those applications. Each add-on specifies which applications and versions it works with, such as Firefox 50.0 - 52.*. For Firefox add-ons, the install buttons will indicate whether the add-on is compatible or not.
What are the different types of add-ons?
There are several kinds of add-ons that customize Firefox in different ways:
Extensions add new features to Firefox or modify existing functionality. There are extensions that allow you to block advertisements, download videos from websites, integrate more closely with social websites, and add features you see in other applications.
Complete Themes change the entire appearance of Firefox, usually including icons, colors, dialogs, and other visual styles.
Themes are lightweight themes that use background images to customize your Firefox toolbars.
Search Providers add additional choices to the search box dropdown. These providers allow you to quickly search any website.
Dictionaries & Language Packs add support for additional languages to Firefox.
How do I install, manage, or remove an add-on?
In most cases, add-ons can be installed by simply clicking the install button provided. Add-ons can be managed, disabled, or uninstalled from the Add-ons Manager in Firefox. For more detailed instructions, read this article on extensions or this one for Themes and Complete Themes. If you have difficulty installing add-ons, see Troubleshooting Extensions and Themes.
How do I keep add-ons up-to-date?
Add-ons are automatically checked for updates once every day. In Firefox, updates are automatically installed by default.
Are add-ons safe to install?
Use caution when installing add-ons, as they may harm your computer or violate your privacy. Add-ons available from this site may be subject to review by Mozilla's team of reviewers, and user feedback is closely monitored, so they should generally be safe to install. Learn more about our review process
Can add-ons make Firefox slower?
Most add-ons do not cause a perceivable performance decrease in Firefox, though installing an excessive number may have adverse effects. If you suspect an add-on is causing Firefox to be slow, try disabling it.
Firefox told me an add-on isn't compatible. Is there a way I can still use it?
If an add-on isn't compatible with your version of Firefox, it is usually either because your version of Firefox is outdated or the add-on author has not yet updated the add-on to be compatible with a newer version you are using. Mozilla does not recommend trying to circumvent these compatibility checks, as they can lead to browser instability or in some cases loss of data. For users who are testing out alpha or beta versions of Firefox, we offer the Add-on Compatibility Reporter to help add-on developers update their compatibility.
What if I have problems with an add-on?
Add-ons are usually created by third-party developers from around the world, so the best way to get help with an add-on is to look for support links on the add-on's homepage or contact the developer. If you are having issues with Firefox that you suspect are related to add-ons you have installed, visit this support article for troubleshooting tips.
Add-on Gallery

How do I choose between add-ons that seem to do the same thing?
There are often several add-ons that have similar features. To figure out which is right for you, read the entire description of the add-on and view its screenshots. If there are still several in the running, read through the add-on's ratings, user reviews, and statistics to see which is most liked by other users. Remember that you can also just try out both and see which you like better.
What if I can't find an add-on I'm looking for?
With thousands of add-ons available, there's something for everyone. But if you're looking for a particular add-on and can't find it, you might try searching on other sites or posting about it in our Add-ons forum.
What does it mean if an add-on is "experimental"?
Experimental add-ons have been marked by their developers as not suitable for a wide audience. They may have bugs or not work properly. Use caution when installing experimental add-ons and uninstall the add-on immediately if you notice problems. Learn more about our review process
What does it mean if an add-on is "not reviewed"?
If you receive a direct link to an add-on that says it hasn't yet been reviewed, it means it's currently awaiting review by Mozilla. Use caution when installing these add-ons, as they could harm your computer or violate your privacy. Learn more about our review process
How much do add-ons cost to purchase?
Add-ons hosted in our gallery are free unless clearly marked otherwise.
What does it mean when an add-on asks for contributions?
Some add-on authors request users who enjoy an add-on to contribute to its development by making a monetary contribution. These contributions go directly to the developer unless a third party is indicated, such as the non-profit Mozilla Foundation.
What are beta add-ons?
Beta add-ons are unreviewed versions which represent the latest work of an add-on author. While different authors have different standards for beta code quality, you should assume that these add-ons are less stable than the general add-on releases.

Please note that when you install an add-on from the "Beta Version" section of an add-on's listing, you will continue to receive updates for that add-on as they become available. Like the initial version you installed, all beta releases are not reviewed by Mozilla and may harm your computer.

How do I report an inappropriate or spam user review?
To report a user review of an add-on, log in with your account and visit the add-on's reviews page. Find the review you wish to report, click "Report this review" and select a reason. Our reviewers team will investigate the review and take appropriate action.
How do I report a bug or contact the Mozilla Add-ons team?
Please visit our Contact page.
What is a Source Code License?
The source code used to create an add-on is an exclusive copyright of the add-on author, unless otherwise declared in a source code license. Many add-ons on this site have open source licenses that make the source code publicly available for copy and reuse under conditions determined by the author. Most authors choose widely known open source licenses like the GPL or BSD licenses instead of making up their own.

Firefox and other Mozilla software are open source.

Collections and Favorites

What is a collection?
Collections are groups of related add-ons created by users to share.
What is the My Favorites collection?
Favorite add-ons are add-ons that you have bookmarked to easily get back to later. You can add an add-on to your favorites collection by clicking "Add to favorites" on its details page.
Mobile Add-ons

What are mobile add-ons?
Mobile add-ons work with Firefox for Android and add or modify functionality just like desktop add-ons. You can find add-ons that work with Firefox for Android in our gallery.
Developer Topics

Please see our Developer FAQ and Developer Hub for answers to add-on developer-related questions.

Still have questions?

For general Firefox support, visit our support website. For general add-on and website questions, visit our forum.