Numbers have to follow exactly the one single format that is recognized by this Add on, or they won't be linkified. +49 123 456789 is detected, but it's not capable handling numbers with special characters as they are customary in Europe like +49 (0) 123 456789 and +49 123/456789. There's no "phone" or custom protocol to use with.

The former Add on "telify" did all this and worked like a charm. But since Mozilla changed the add on API many many extremely good and helpful add ons are gone without replacement.