I am trying to upgrade the firmware on my 120 and it has been running in Safari for 40 minutes! This seems abnormal. How do I know if it has finished?

Seems like Safari was the issue - in the end I took the plunge and disconnected - the modem was still on the previous version firmware. Tried the upgrade using Firefox and it went through in seconds.

So, all you Mac users - don't upgrade firmware using safari - you'll be sitting a long time!