.XPI File Extension

Cross-platform Installer Package

Developer Mozilla
Popularity
4.0  |  760 Votes
Category Plugin Files
Format Zip

What is an XPI file?

An XPI file is a compressed installation archive used by various Mozilla applications, including Firefox, Thunderbird, and SeaMonkey. It contains an app add-on, such as a Firefox plug-in, toolkit, or theme. Most XPI files include an install.js, install.rdf, or readme.md file, which contains the add-on's installation instructions.

More Information
Screenshot of a .xpi file in Apple Finder
XPI file open in Apple Finder

XPI files are essentially renamed .ZIP archives that Mozilla applications use to install add-ons. These archives often contain .JS, .CSS, .HTML, and .JSON files that, combined, comprise the code needed to install an add-on. Add-ons that use icons and other images also contain .PNG files.

How to open an XPI file

Some versions of Mozilla Firefox allow you to install an XPI file by dragging and dropping the file onto an open browser window. Firefox then uses a component called XPInstall to install the add-on your XPI file contains.

If dropping your XPI file onto Firefox does not work, you can manually install the file using the instructions below:

  1. In Windows, select the Menu (three horizontal line) icon in Firefox's upper-right corner and click Add-ons. (In macOS, select Tools → Add-ons.)
  2. Select Extensions, Themes, or Plugins (depending on the type of add-on your XPI file contains).
  3. Click the Gear icon dropdown menu and select Install Add-on From File....
  4. Navigate to and select your XPI file. Then, click Open.

How do I install an XPI file in the mobile version of Firefox?

On Android devices, you can install the add-on an XPI file contains by locating the file in an Android file manager (such as File Viewer Plus or ES File Explorer), tapping it, and opening it with Firefox.

The iOS version of Firefox does not allow users to install XPI files.

How do I install an XPI file in Mozilla Thunderbird?

To install an XPI file in Mozilla Thunderbird:

  1. In Windows, select the Menu (three horizontal lines) icon, click Add-ons, and then click Add-ons again. (In macOS, select Tools → Add-ons.)
  2. Select Extensions, Themes, or Plugins (depending on the type of add-on your XPI file contains).
  3. Click the Gear icon dropdown menu and select Install Add-on From File....
  4. Navigate to and select your XPI file. Then, click Open.

How do I view an XPI file's contents outside Mozilla applications?

Since an XPI file is a Zip-compressed archive, you can manually extract and view its contents by:

  1. Renaming the file to use the .zip extension.
  2. Extracting the file's contents with a Zip compression utility, such as Corel WinZip (Windows, Mac), 7-Zip (Windows), or Apple Archive Utility (Mac).
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Programs that open or reference XPI files

Updated December 13, 2021

Verified by FileInfo.com

The FileInfo.com team has independently researched the Cross-platform Installer Package file format and Mac, Windows, Linux, and Android apps listed on this page. Our goal is 100% accuracy and we only publish information about file types that we have verified.

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