[gcp]

Advertising income due to selling the default homepage and search boxes. In case of Opera and Mozilla Corporation, the majority of that income is from Google (who calls this "traffic acquisition costs" in their accounting).

Opera also licenses their browser to many phones and devices. That market may be starting to dry up.

[objclxt]

Opera actually has a substantial sideline in selling mobile advertising, just like AdMob et al. I know this because my current employer spun-off our mobile ad network, which Opera then bought.