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

>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)

Works like charm.

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)

This extension is absolutely amazing. I consider it one of the very select "Absolutely Mandatory and Indispensable" extensions I always use. I truly do not know how I lived without it, before first finding it. I don't know why Mozilla isn't pushing this as one of the *Recommended* extensions, because it should. Maybe I'm overestimating the number of people who would be interested in launching a webpage from one browser directly into a specific other browser, but for those that ever do this more than occasionally, this thing is terrific. I love Open With so much.

A little messy to install, but very useful when you get it going.

Works perfectly on Manjaro Linux! The AMO page should mention that the extension requires additional setup after installation. It took me a while to figure out that I need to go to the Options page after installing the extension.

A little touchy to install it for a newbie like me...
But once you follow the instructions given, it work like a charm!
Thanks a lot from a Waterfox Classic user.

AWESOME! I wanted such an extension for a long time! The best part? It supports Linux, unlike some other similar extensions! :D
This extension has a HUGE potential! I just added SMPlayer to watch YT vids in it and damn - it works! :D :D

Thank you for a very nice add-on.
I have one request, but I want you to be able to export the settings

La verdad es fácil la instalación y funciona correctamente. sería bueno que estuviera para los demás exploradores.

Excellent add-on. Installation requires a few extra steps, but the instructions are very clear. Deserves donations.

I kept checking back to the reviews in hopes of more info on the installation of "open with", and there it was. I put open_with_windows.py in my Windows\system32......opened a command prompt, which opened in the Windows\system32 folder, and ran the open_with_windows.py install, and that was it for me. I ran test installation in my Browser and Thunderbird, and it showed, "Found version 7.2.3 at C:\​Windows\​System32\​open_with_windows.py." I then edited the order of my four Browsers, with Firefox on top.
Thanks to all the reviews with the help, and thanks to the the Author of this addon!!