Hello,
I have tested it on 3 different machines and 3 different devices, two Airport Extremes (2013) and One Time Capsule (2013).
If you update your Airport Firmware to 7.7.8, you would not be able to access your files directly from finder in your Mac Sierra (10.12.2) .
Apple has messed up something either in this firmware or 10.12.2 macOS update.
I have tested it on 3 different machines and 3 different devices, two Airport Extremes (2013) and One Time Capsule (2013).
If you update your Airport Firmware to 7.7.8, you would not be able to access your files directly from finder in your Mac Sierra (10.12.2) .
Apple has messed up something either in this firmware or 10.12.2 macOS update.