Yahoo Inc will fire at least 1,500 workers to cope with a crumbling economy that dented its third-quarter profit and turned up the heat on the slumping Internet company’s management as investors stew over a missed opportunity to sell to Microsoft Corp for $47.5 billion. The purge outlined represented a 10 percent reduction in Yahoo’s payroll of about 15,000 employees. It’s the second time in nine months that Yahoo has resorted to mass layoffs in what so far has been an ineffectual effort to rebound from a financial funk that has left its stock price near a 5-year low. Yahoo’s housecleaning, to be completed by the end of the year, provides the latest example of how a credit crisis that has already rocked banks and retailers is starting to rattle Silicon Valley, America’s high-tech heartland. Online auctioneer eBay Inc is jettisoning 1,600 jobs while an array of startups are letting go of workers to squirrel away more cash as venture capitalists become more cautious with their money. Even Google Inc, a company renowned for its free-spending ways, is starting to cut corners.