The continuing shifts in browser usage should show vendors not to take their status for granted, Gardner said.

"It indicates how quickly people will move to a new software when they have that choice," he said. "To think that there's a great deal of security in your market position is not something to be lazy about. People will go somewhere else that will better suit their purposes."

Carol Baroudi, an analyst at Hurwitz & Associates in Waltham, Mass., said another reason for the growing use of Mozilla is that it's open-source software.

"For a lot of people, Mozilla happens to be a political choice," Baroudi said. "And IE has been problematic" with viruses, spyware and other security issues, she added.