Think OpenDNS, when a user types in a non-existent domain OpenDNS returns a Google search results page which offers some suggestions and make money off of the ad revenue.I'm not certain what you mean about NXDOMAIN catches, can you elaborate? Basically what I was envisioning was having the Tun device forward .bit traffic to a local SOCKS proxy (like the proxy part of FreeSpeechMe) via something like Tun2Socks.
Well, I don't think we should distribute a Tor Browser Bundle version : )Automating builds of a "Namecoin browser" is one thing, making sure they're reproducible is something else, because ideally you would need multiple developers running the builds on their own machines. That's difficult to automate. Maybe I'm unaware of something, but I believe even the Tor Browser Bundle is not built automatically.
However, whatever our process, we should just download the binaries from Mozilla proper and then add in our own extension. No need to have a reproducible build there, just check the hash to make sure it matches Mozilla's published hash. : )