Can Firewalla see my private data?

If you are talking about data inside of packets, such as photos, bank account balances, texts, etc...

NO, we do not and cannot see what's inside. And we wouldn't even if it was possible. 

Firewalla operates by ONLY looking at the IPv4/IPv6 packet header. Using just that piece of data, we can get a good estimate of each device's activities.  

In addition to the packet header, Firewalla can see mapped DNS addresses, clear text, and a bunch of other metadata. This is all our app can see.

The Firewalla Cloud will see mostly hash data. Something like this:

To learn about how the Firewalla Cloud works in Active Protect, please see https://help.firewalla.com/hc/en-us/articles/360049856394-How-to-Secure-Your-Network-with-Firewalla-Part-3-Protect