Instruction for installation is insufficient, only thanks to user f495dc (not far below) i managed to install this app

i repeat it again here

1. Install Python (Download from link, run file, and then follow install screens)
2. Download the linked .py file and then move it to a special folder or the root of your C:/ drive (I put mine under the python install folder/Lib)
3. Open a Windows Command prompt (Type command or cmd into Start Menu search and select the cmd.exe)
4. Navigate inside the command prompt to the folder where you put the file in #2 (i.e. "cd c:\path_of_file_folder")
5. Run the command given in instructions: "open_with_windows.py install" (You must be in the same folder as the file)
6. Click Test in the extension info screen inside of Firefox. It will tell you immediately if it worked and you can begin finding/adding external programs to launch