Mozilla Corp., which oversees development of the popular Firefox Web browser, has promoted John Lilly to chief executive officer. Lilly took on the new job Monday after serving as Mozilla's chief operating officer since August 2006. Lilly previously worked at Apple Inc. Sun Microsystems Inc. and software startup Reactivity before joining Mozilla in 2005 as vice president of business development. "I feel both very excited and very fortunate to find myself in this spot, and am looking forward to doing what I can to help Mozilla continue to make the Web a better place," Lilly wrote on his blog Monday.

Mitchell Baker, Mozilla's previous CEO, will remain chairman of the Mountain View-based company, which operates as a subsidiary of the nonprofit Mozilla Foundation.

Mozilla is best known for the Firefox browser, which it says has about 125 million users. Firefox has a loyal following among Web surfers looking for an alternative to Microsoft Corp. s dominant Internet Explorer Web browser.

"John Lilly is the right person to guide the maturation of Mozilla," Baker said.