So, if you want to override the users choice of browser, it's acceptable if you first replace "https://" with "microsoft-edge://" ? They're doing the exact same behavior, just with two steps instead of one.
So to answer your question, yes. If a program is specifying "firefox://" and using it to mean "https://", then that should be considered a bug in the program specifying it. That bug can either be fixed in the program itself, or can have a workaround in an external program.