Amazon.com Inc. shares surged Friday, lifting its founder’s net worth by $7.8 billion to $91.3 billion as of 10 a.m. in New York, according to the Bloomberg Billionaires Index. The stock climbed 10 percent to $1,070.59, after the retailer reported results that beat Wall Street estimates. If the share gains hold through Friday’s close, Bezos will top the index for the first time. His wealth briefly surpassed that of Microsoft Corp. co-founder Bill Gates on an intraday basis on July 27, but Amazon shares ended the day lower, leaving Bezos at No. 2.