That said, there's no need to report it since it's not going to get fixed (by Opera).
You are right about Opera's update causing this since Opera is now a 64-bit browser on Mac. Garmin needs to provide a 64-bit plugin if they want it to work with newer browsers. So you should report it to them.
Thanks christoph for trying but... Safari has been a 64-bit one for a while and it works there with no problem.
Anyway, Opera got updated just yesterday. Looks like they've fixed something and it's working now.