Thunderbird and Firefox refuse to open existing profile after upgrade 15.2->15.3

Hi, Yesterday I upgraded my sister's system from 15.2 to 15.3 After that, both Thunderbird and Firefox refuse to open te existing profiles. Gives the message "You are starting with an old version of ". Which is an odd messages, because one would expect TB and FF to be newer, not older, after the upgrade... Anyone an idea how to solve this? regards, Jogchum Reitsma