HomeHow ToWhat is an XPI File and How to Open It?

What is an XPI File and How to Open It?



Do you wonder what an XPI file is all about and how do you use it? Well, you’re in luck as we will be talking about it in today’s post.

What is an XPI File?

A Cross-Platform Installer Module (XPI) file is simply an archive file used by applications such as Firefox, Thunderbird, and SeaMonkey – all under Mozilla. It a compressed installation file for a web browser plugin, extension, theme or Thunderbird dictionaries.

Apart from the actual software installation file which is usually packaged as a JAR file, an XPI archive also contains an install.js or install.rdf. These additional files contain the installation instructions.

Firefox allow you to install XPI (pronounced “zippy”) files by simply dragging and dropping the file onto an open web browser window. The Mozilla software uses a component called XPInstall, (which includes Mozilla installer script) to install the XPI packages. Once downloaded and dropped into an extension manager, the installation instructions contained in the XPI, is being read and executed by XPInstall.

XPI archives only support files stored uncompressed or compressed using the “deflate” method.

How Can I Open an XPI File?


As we mentioned above, you need a suitable Mozilla software to open the XPI file. Most commonly, the Firefox browser is being used for this purpose.

A Windows error message that says “How do you want to open this file?” on Windows 10 or “Windows cannot open this file” on Windows 7, will pop-up if you try to open the file using a non-Mozilla software.

If dragging and dropping gives you an error in installing an XPI file, try this:

  • Right-click or long-press on the file.
  • Click “Open with” and choose the Firefox app.

How to Convert an XPI File

For some reasons, you might want to know if you can convert an XPI file to another archive format. Unfortunately, the answer is no. Other browsers have a similar archive file format for their extensions but these cannot be easily converted from one to the other as they are built using different algorithms and formats.

Chromium-based browsers such as Google Chrome, Brave, Opera and Microsoft Edge use CRX, while Safari uses SAFARIEXTZ. All these file extension archive file formats cannot be used to install add-ons in Mozilla Firefox. Same is true with the XPI, it cannot be used in those other browsers.


For SeaMonkey which uses much of the same Mozilla Firefox source code, you can use a tool called Add-on Converter for SeaMonkey. This online tool will convert an XPI file that is compatible with Firefox or Thunderbird into an XPI file that will work with SeaMonkey.

How to Create an XPI File

You can use any method to create a .zip file, which you can then rename to .xpi. It is important to note the requirement that only one compression method is supported – “deflate”, but files can also be added to the archive in uncompressed form.

Top-level files such as those that inside manifest.json (WebExtensions) or chrome.manifest and install.rdf must be in the root directory of the archive, not in the subdirectory.

To learn more on how to efficiently create XPI installer modules click here.


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