Installing Firefox plugins issue

I am trying to install my own firefox plugin. I follow this tutorial. But each time thi开发者_开发知识库s gives me following error:-

Firefox could not install the file at 

file:///home/ubuntu/googbar.xpi

because: Install script not found
-204

That error means that your file doesn't have an install.rdf file. Please note that it needs to be at the top level of the XPI archive. So maybe you made a mistake packing the file and install.rdf landed in a subdirectory. You can check the list of files using unzip -l googbar.xpi command, it should list install.rdf without a directory name before it.