Ubuntu add repo app-key fails
Just ran into a very simalar problem and by deleting the problem key in /etc/apt/trusted.gpg.d/{Problem-Key}.asc I was able to solve the issue!
Hope this helps!
This is because GPG parses keyring paths containing colons as URLs (yeah, I don't know about that either).
Try the following:
mv /etc/apt/trusted.gpg.d/home:hawkeye116477:waterfox.asc /etc/apt/trusted.gpg.d/home_hawkeye116477_waterfox.asc