WASHINGTON, July 15 (Reuters) - U.S. Treasury Secretary Janet Yellen said on Thursday that it was not certain that Amazon.com will reach the profitability threshold for a new global tax deal that would allow more countries to tax large multinational firms. “It depends on whether or not they reach the threshold of profitability and I’m not certain of that,” Yellen told CNBC in an interview when asked whether the 132-country agreement would reallocate taxing rights for Amazon. (Reporting by David Lawder and Diane Bartz; Editing by Leslie Adler)