Problem solved, but no idea what changed
 

The neighbor's computer, using Ubuntu 12.04, could connect to the modem through a router both wireless and wired. I could ping the computer from my smart phone through the router. ifconfig showed no problems. IPv4 addresses assigned, no errors, etc.

The problem: no browser could connect to an outside site. They just timed out. I checked the browsers' connection methods. No luck.

The solution: I also needed to install a printer. I used the System Settings Printer Configuration. When the computer downloaded a driver the progress bar stuttered a bit and then proceeded across smoothly. The driver was installed and the printer works.

With only that activity, the browsers now can access the WWW.

Any ideas as to what hidden switch CUPS(?) might have flipped to get the driver???

Sorry I don't have more hardware configuration details. The computer is a neighbor's. The router had wireless, but no visible antenna, and the modem is a Gilat SkyEdgeII satellite modem (Australia's NBN).

Was it using DHCP? I ran into a similar problem when assigning a static IP and didn't have DNS set correctly. The machine would connect to the network but wouldn't load a webpage. I finally got the DNS sorted out and that fixed it.

I'll have to check on that. I'm reasonably sure DHCP is used.