title: firefox add on can't be installed
body: <p>I program firefox addon. I try to install xpi file from official tutorial and it works. I copy xpi file. I try to install copied xpi file. I don't change any files in the xpi file. The installation doesn't work. firefox says copied xpi file is not working. I don't change anything it's exactly the same file. Why doesn't this work:?</p>
  
  <p>info: I found out that somebody had same problem. He copied the extracted folder that appeared after extracting xpi file. When he copied the content of the folder, it worked. I copy content of the folder all the time but it doesn't work.</p>