XPI stands for compressed files which are used for a variety of Mozilla Firefox web browser applications. The files are created by different Mozilla applications, including Thunderbird email, and are similar to compressed zip files. When XPI files are accessed, they automatically unpack and install browser extensions for Mozilla Firefox or Thunderbird email.
XPI files will vary in content since they are used as a plugin for a variety of different applications. The files are installed by simply dragging and dropping into the Firefox browser or by clicking on File on the main toolbar and then choosing the Open option to install an XPI file.
The XPI file is also known as the Mozilla Installer Package and is an archive associated with XPInstall. XPInstall is a cross platform installer which is used for installing extensions in Mozilla Firefox, SeaMonkey, Thunderbird, and Mozilla Application Suite. It contains an install script at the root of the file in addition to other data files in the XPI format.
How to Open XPI Files
There is really no reason for opening XPI files except for use with the above named applications and programs. However, if you are a programmer, you can open and view the contents of an XPI file by right clicking on the file and choosing Open With from the drop-down menu. Choose a text editor such as NotePad or TextEdit from the submenu and then proceed to open the file using this program.
If you use the Windows operating system or Mac OS X, you will need to use XPInstall. It is typically included with the Mozilla Firefox web browser. You can also open XPI files using Mozilla Thunderbird or SeaMonkey.
For the Linux operating system you can use Firefox, Thunderbird, or SeaMonkey for opening and using XPI files.
It is also possible to open XPI files by changing the name of the file extension to ZIP. Since XPI files are compressed files, you can open and view the contents using a program such as WinZip, but first you should change the extension. To do this, it is necessary to locate the file in Windows Explorer or any file management program used with your operating system.
Once you locate the XPI file, right click on it and choose Rename from the drop-down menu. In the new command prompt change the extension to .ZIP and then close the window. If you have a program such as WinZip installed on your PC, it should automatically open and unzip the XPI file by default to allow you to view the contents.