Opera Software ASA announced Tuesday that co-founder and CEO Jon von Tetzchner has stepped down following 15 years at the helm of the Norwegian software developer.

The company has tapped Lars Boilesen, chief commercial officer, to lead the company known for the popular Opera internet browser.

The statement did not give any specific reason for von Tetzchner's decision but said he would continue to serve as a full-time "strategic adviser."

"My decision to assume a new role in Opera is based on a lengthy consideration process," von Tetzchner said in a statement.

Opera's chief strategist, Rolf Assev, said von Tetzchner's decision had nothing to do with the company's recent poor performance. He said the former CEO, who has three children, wanted a more flexible position to cut down on travel.

Opera disappointed analysts and investors in November with a third-quarter loss of 12 million kroner ($2.1 million) and lower-than-expected revenue.

Shares in the software company rose 4 percent, to 20.80 kroner ($3.66), in midday trading Tuesday in Oslo.

In the late 90s and early 2000s, the Opera browser was a strong alternative to Microsoft Corp.'s Internet Explorer and Time Warner Inc.'s Netscape, but its popularity diminished with the rise of another rival, Mozilla's Firefox.

Oslo-based Opera employs 760 people in 10 countries. In June, the group launched its first file-sharing feature, Opera Unite, which allows users to share photos, music and other files with one another directly, bypassing the need for outside services such as Facebook and Flickr.