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How to sideload an add-on in Firefox

Add-ons for Firefox are generally available in the Firefox Marketplace along with themes. These add-ons are safe and you can install them with a few clicks. It’s about as easy as it gets. Add-on developers generally do not have to face any problems when they submit an add-on so distribution is fairly simple.

That said, not all add-ons are distributed via the Firefox Marketplace. Some will inevitably have to be distributed from outside it. In order to install these add-ons, you have to side-load them. Here’s how.

Sideload an add-on

Sideloading an add-on in Firefox is really easy. All you need is the add-on file which is an XPI file. Developers choose how they distribute their add-ons which is why we can’t point you to a single place where add-ons from outside the Firefox Marketplace are made available. They may be on a developer’s website, or they may be on a Github page.

Once you have the XPI file, all you have to do is drag & drop it on to an open Firefox window. Alternatively, you can tap the Ctrl+O keyboard shortcut to open the Select File box, and then select the XPI file from it.

You will see a prompt asking if you want to add the add-on to Firefox, and it will show you a list of the permissions it will have access to. Click Add, and it will be installed.

To uninstall an add-on that you sideloaded, tap the Ctrl+Shift+A keyboard shortcut. This will take you to the add-on manager. Click the more options button next to the add-on and select ‘Remove’ from the menu.

Limitations & precautions

Add-ons that are not from the Firefox Marketplace may not be safe. If the add-on is open-source, it’s likely going to be harmless but if it isn’t, make sure the developer is reliable before you sideload an add-on. A malicious add-on that you install to your browser can steal all sorts of information.

This method will not allow you to install add-ons that are not compatible with your version of Firefox. Compatibility hasn’t been a problem with Firefox add-ons for a long time but there will still be exceptions. If you find an old add-on’s XPI file, and try to install it this way, it may not work. It might also install but fail to work as it should. If that’s the sort of add-on you’re trying to install, it’s best to seek an alternative for it.

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