CREATE .XPI FILE FROM ALREADY INSTALLED FIREFOX ADD-ON

• To create .xpi file for any extension, install that extension in Firefox browser from Get Add-ons.
• Install FEBE or OPIE Firefox extension in Firefox browser from Get Add-ons.
  
  
  
  
  
  
  
  
• Export existing Firefox extension using the above extensions.

Read more about HOW TO ADD AN ADD-ON TO FIREFOX INSTANCE OF SELENIUM WEBDRIVER?