Instead of opening links with the default profile, FF should open it with the currently used profile (in case any FF instance is running). Otherwise, it should open it with the default profile.
Demo: On Windows. FF is default browser. There are two profiles: 1) "work" which is default and 2) "personal"
Open any hyperlink (from an email, a document or elsewhere). independant whether no FF instance is running or an FF instance of the "personal" profile is running, the result will be: a new FF instance of the "work" profile will start and open the link. => This seems not to be the correct or expected behaviour.