Thieves broke into a lighting store in Grass Valley and used the business’ own dolly to make off with a 6-foot bronze Tiffany lamp that retails for $10,000. David Boynton, the owner of Illumination The Lamp Doctor on East Main Street, discovered the break-in New Year’s Eve morning, according to dispatch reports. “They threw a big rock through the front plate glass window,” said Boynton’s stepfather, Arnold Goldberg. “They managed to get the cash register opened, which had a spare door key.” They then opened the front door and used the dolly to steal the lamp, which Goldberg said weighed …