It seems like the main parabolic application needs to be closed for the extension to be able to add a download. If the program is already opened the download the extension tries to add is never added. At least this is the case on my Win 10 machine.

An absolutely astonishing app and extension! Absolutely recommend it to anyone who feels that content, music, media is too centralised and locked within platforms. You can find the app here on github

Nice extension.
[It would be great to be able to remove its entry to the right click context menu. Unfortunately, Firefox has no native way to do this, so the extensions have to provide this option.]

Edit: It's possible (see developer's response)

it's gtk and not native (because it's flatpak) but it's best yt-dlp gui on destktop marketing

Works well for me on windows 11. Requires the fully installed version, portable doesn't work, if anyone was wondering. My only 'problem' is that every file seems to open another Parabolic.exe, instead of checking if the program is already open, but I hope this gets adjusted in any future updates.