I love it. 👍👍👍
But there is one problem. In Firefox for Mac, if I select Safari that is not running, the URL will open in Firefox as well.
Open With 7.2.5/open_with_mac.py 7.2.4/Firefox for Mac 86.0/macOS 10.15.7

Finally, the installation is successful,Set the default open mode to Python,and use "open_with_windows.py install"
in the folder where the file is located. If you open any other windows when use "open_with_windows.py install" ,you should set the default open mode of .py file. Chinglish

Thanks for the Plugin! Good but complicated. Have written a small tutorial in english and german. Maybe it helps someone.

DE: Gut aber kompliziert zu installieren. Wer Hilfe braucht kann es mit der kleinen Anleitung versuchen.

https://plugins.onkel-franky.de/tests/other-stuff/tutorial-firefox-plugin-open-with

Great add-on, but open with Edge doesn't work.

Would be nice if it works with bookmarks too.

Works great, and the Python Script is much better than the binaries required by other tools. That said, I'd prefer a solution without additional install, but that unfortunately doesn't seem to be possible with the new add-on framework :/

I suppose that it comes down to this: is installing python a pain in the ass? If you think so, avoid this extension. Otherwise, this extension is great!