Thank you for reporting this to Ubuntu. While .xpi files are used in Firefox, there are also used in other applications based on xulrunner such as Thunderbird or Songbird. It is not clear from the extension which application should be opened. Therefore, I am marking this as won't fix.
Please feel free to report any other issues you may find.
Thank you for reporting this to Ubuntu. While .xpi files are used in Firefox, there are also used in other applications based on xulrunner such as Thunderbird or Songbird. It is not clear from the extension which application should be opened. Therefore, I am marking this as won't fix.
Please feel free to report any other issues you may find.