What is the possibility or probability that a relay that my browser is using can see and record my traffic?
It's mainly the exit node you'd need to be worried about, as that's where the last layer of encryption added by Tor is stripped off. The other two relays in your circuit (i.e. the entry node and middle node) can't see what's going on because of the encryption added by Tor before it leaves your computer.
So what about the exit node? As Alexey says, the Tor Browser comes with HTTPS-Everywhere enabled by default, and therefore enforces the use of HTTPS (i.e. TLS). Attempts to connect to sites that don't support HTTPS will generate a warning and be prevented. This means you're safe from Man-in-the-Middle attacks by rogue exit nodes.
However, there are other things you should be aware of when assessing your threat model, such as correlation attacks. There's a page on the Tails site (an OS that enforces the use of Tor for all network connections, not just the browser) that would be worth reading in understanding the other threats.
the probability is 100% at exit node =) It's an exit node who receives a packets that it sends for you outside. But if you're using SSL/TLS verification - you should not worry about any interventions in your network traffic. About a plaintext traffic there's nothing unusual : it IS insecure, inside Tor, outside Tor or even in your home LAN.