bill001g :
In general the firewall does nothing by default it is set to allow everything. There may be some minor rules that attempt to prevent attacks against the router itself.
I suspect more you want to get rid of the double nat.
It depends on the device att provides...I am too lazy to look it up. You want to put it in bridge mode which makes it only a modem. Problem is many of the att uverse offering you can not do that. This is especially true if you get tv from them because the router is used to get information for the set top boxes. You best hope in those cases is to put your second router in the DMZ of the att device. You will still have 2 levels of nat but it does solve some issues related to double nat.
Yes, I'm trying to get rid of the double NAT, which I know has to be possible. About Uverse, even if I made it into a bridge, it should still work because I have it hooked up into the Ethernet on the back. I've tried to look into the bridge mode on my modem/router but I've not found anything that links to it. When I was troubleshooting my Netgear router I asked the assistant if she knew how to do it, she said yes, but couldn't do it due to restrictions. Anyway, she said to do something along the lines of a full bridge mode with a public IP address. Not sure how to do that though, so any help would be nice