Open With is one of the few remaining Firefox extensions that are both extremely useful and actually working as designed. After downloading, follow the steps in the Open With Options page to install it.

First, use the "Fetch it from here" link to download the latest version of the Python software. Click on the downloaded installer to install Python. By default, it will install to C:\Users\[username]\AppData\Local\Programs.

Second, use the "Click here to download" link to download the Python file opem_with_windows.py. Move the file from the Downloads folder to the folder where you want it to be installed.

Third, use Command Prompt to install the .py file. It's a 2-step process. First, you have to tell Command Prompt where you put the file. Then you have to tell Command Prompt to install it.

For example, if you moved the .py file to C:\Users\[username]\Firefox, then the first command you would type in Command Prompt would be

cd "C:\Users\[username]\Firefox"

Press Enter. Then type

open_with_windows.py install

Press enter. Close Command Prompt.

Now, in the Open With Options page, click the "Test Installation" button. If a green check mark appears, you're done. If a red "X" appears, repeat the steps above until you get it right.

IMPORTANT NOTE: Understand that the Python software you downloaded enables the Python .py file to function, and the .py file enables the Open With extension to work. If you rename or move the folder in which you installed the .py file, the extension will stop working. In that case, use Command Prompt as above to reinstall the .py file in the new or renamed folder location.