Tokyo stocks opened mixed Friday, as selling tracking overnight falls in U.S. technology shares was offset by buying of exporters on a weaker yen against the U.S. dollar. In the first 15 minutes of trading, the 225-issue Nikkei Stock Average dropped 47.25 points, or 0.14 percent, from Thursday to 33,492.37. The broader Topix index was up 4.43 points, or 0.19 percent, at 2,366.45. On the top-tier Prime Market, decliners were led by mining and electric appliance issues, while transportation equipment and insurance issues led gainers. At 9 a.m., the dollar fetched 141.42-45 yen compared with 141….