Addon Download:
https://addons.mozilla.org/en-GB/firefox/addon/external-application/

Also required:
https://github.com/andy-portmen/native-client/releases
download, then unzip, then run installer

Example for dl option using remote yt-dlp

Name: Download with yt-dlp on gondor
exec: gnome-terminal
args: --  ssh gondor "cd Downloads; ./yt-dlp_linux [HREF] ; echo ''; echo 'press enter'; read line"
Toolbar, page and link context