Thank you for the very thorough reply! For god knows what reason I get this error: error: app/org.mozilla.firefox/x86_64/stable not installed when running the xdg-open firefox-reader command, yet manually running flatpak run --user org.mozilla.firefox about:reader?url=https://example.com works just fine. I’ll have to troubleshoot it when I have a bit more time ;p
Thanks again for your very thorough write up and the linked articles. Have a good day :)
Update: It seems like on my system, the –user flag was the issue, removing it made the script function. I am using Fedora Kinoite (Immutable version of KDE Plasma), so perhaps it is just a difference in how flatpak is configured between distros? I’ll have to read into it more later.