That sounds awesome. Can you share your repo, if it's public?
May I suggest you to add a small (and optional!) config file to automate your UI - like e.g.:
[Sources]
Telegram=chrome profile B
Discord=epiphany
[Destinations]
https://www.google.com=firefox profile A
If the config is there, you'd then only show the UI when neither sources nor destinations match (regexes). This would make it a must have tool IMHO :)