What Is an XPI File?

How to Open, Edit, and Convert XPI Files

XPI Files
XPI Files.

An abbreviation for Cross-Platform Install (or XPInstall), a file with the XPI file extension (pronounced "zippy") is a Mozilla/Firefox Browser Extension Archive file used to extend the functionality of Mozilla products like Firefox, SeaMonkey, and Thunderbird.

An XPI file is really just a renamed ZIP file that the Mozilla program can use to install the extension files. They may include images and JS, MANIFEST, RDF, and CSS files, as well as multiple folders full of other data.

Note: XPI files use an uppercase "i" as the last letter of the file extension, so don't confuse them with XPL files that use an uppercase "L" - these are LcdStudio Playlist files. Another similarly named file extension is XPLL, which is used for Pull-Planner Data files.

How to Open an XPI File

The Mozilla Firefox browser uses XPI files to provide extensibility in the browser. If you have an XPI file, just drag it to any open Firefox window to install it. Mozilla's Add-ons for Firefox page is one place you can go to get official XPI files to use with Firefox.

Tip: If you're using Firefox when you browse for add-ons from the link above, choosing the Add to Firefox button will download the file and then ask you to install it right away so that you don't have to drag it into the program. Otherwise, if you're using a different browser, you can use the Download Anyway link to download the XPI.

Mozilla's Add-ons for Thunderbird provides XPI files for their chat/email software Thunderbird.

These XPI files can be installed through Thunderbird's Tools > Add-ons menu option (or the Tools > Extension Manager in older versions).

Although they're now discontinued, the Netscape and Flock web browsers, Songbird music player, and Nvu HTML editor all have native support for XPI files.

Since XPI files are really just .ZIP files, you can rename the file as such and then open it in any archive/compression program.

Or, you can use a program like 7-Zip to just right-click on the XPI file and open it as an archive to see the contents inside.

If you're wanting to build your own XPI file, you can read more about that on the Extension Packaging page at the Mozilla Developer Network.

Note: While most XPI files you come across will likely be in a format specific to a Mozilla application, it's possible that yours has nothing to do with any of the programs I mentioned above, and instead is meant to be opened in something else.

If your XPI file isn't a Cross-Platform Install file but you don't know what else it could be, try opening it in a text editor like Notepad++. If the file is readable, then your XPI file is simply a text file. If you can't make out all of the words, see if you can find some sort of information in the text that can help you determine what program was used to create the XPI file, which you can then use to research a compatible XPI opener.

How to Convert an XPI File

There are file types similar to XPI that are used by other web browsers to add extra features and capabilities to a browser, but they cannot be easily converted to and from other formats for use in another browser.

For example, although files like CRX (Chrome and Opera), SAFARIEXTZ (Safari), and EXE (Internet Explorer) can all be used as add-ons to each respective browser, none of them can be used in Firefox, and Mozilla's XPI file type cannot be used in any of these other browsers.

However, there is an online tool called Add-on Converter for SeaMonkey that will attempt to convert an XPI file compatible with Firefox or Thunderbird into an XPI file that will work with SeaMonkey.

Tip: If you want to convert XPI to ZIP, keep in mind what I mentioned above about renaming the extension. You don't have to actually run a file conversion program to save the XPI file to the ZIP format.

More Help With XPI Files

See Get More Help for information about contacting me on social networks or via email, posting on tech support forums, and more. Let me know what kinds of problems you're having with opening or using the XPI file and I'll see what I can do to help.

If you need development support for your Firefox extension, I won't be able to help with that. I highly recommend StackExchange for that sort of thing.