code: def install_addon(self, path, temporary=None):
          
          payload = {"path": path}
          if temporary is not None:
              payload["temporary"] = temporary
          return self.execute("INSTALL_ADDON", payload)["value"]
docs: Installs Firefox addon.
  
          Returns identifier of installed addon. This identifier can later
          be used to uninstall addon.
  
          :param path: Absolute path to the addon that will be installed.
  
          :Usage:
              ::
  
                  driver.install_addon('/path/to/firebug.xpi')