No longer maintained. Gemini reports the Python file you need to execute as:

"The script's primary purpose is to allow a browser extension to execute commands on the local machine. This capability, while useful for legitimate purposes (like opening files with specific applications), inherently carries a security risk. The direct execution of receivedMessage without apparent input validation is a critical vulnerability."

The only and best add-on for the declared purpose.

Several years ago the developer stopped supporting his plugins to focus on Thunderbird. I hope he isn't the one responsible for how bad Thunderbird is now, because if so he should have stuck to plugins.

>3. Open a command prompt. Run the file with the argument "install", like this:
>open_with_windows.py install
>If you move the file, you must run this step again.

Note for the noobs like me: The command should be:
python open_with_windows.py install

Works well, just follow the installation instruction (native client)

Used to be one of my favorite addons. Did not use it for a long time.

Discontinued by developer, so move onto something else. And it no longer works, and no point in trying to find out why.

Works like charm.

As noted in the "About this extension" section and on the Github repo, this is no longer maintained as of 2022. Further, it doesn't seem to work for many people. For myself, it doesn't work on an m2 mac with Firefox 114.

Could not get the extension to work. No debug codes were given in the firefox browser console, python console or CMD console

The addon is now archived (no more updates).
If it breaks in the future try the following alternative addon:
External Application Button
(by Andy Portmen)

I heard that the "Open With" developer no longer maintains the extension (I hope that some developer continues to update and maintain the extension, as it is very useful to open YT-DLP and video players such as MPV, PotPlayer, VLC and MPC- HC)

A great app! Has somebody found a way to use it with Snap Firefox?

Only for Unix geeks. I'm no newbie, but have tried absolutely everything on here and it simply will not install. Latest version of Python? Check. ---Terminal commands: can only get it ti recognise if I drag the .py file onto terminal. Then, install sill not run no matter the combo. 'Command not found'. This should be part of T-Bird's BASIC setups.

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.