Hello pbiii14, try to opening it from the File menu.

(or save the ".xpi" file extension to your win 7 and dragging it into any Firefox window)

thank you

See also:

• http://kb.mozillazine.org/Installing_extensions

If you are referring to opening an .xpi file to inspect its contents or to modify the contents ......

First off, if you open an .xpi file that is a signed extension, you will break the "signature" and if you change anything in files inside of that extension it won't install in to Firefox. Unlike over a year ago users can no longer modify an extension without getting it signed again.

A zip-utility such as 7-ZIp can be used to open .xpi files. And for reassembly don't use any compression.