@tokyo_0
All browsers are funded by some sort of advert. Firefox's main revenue comes from Google, just by making google the default search engine. They also probably get paid by ebay and others for including them in the search engine list or by adding them to quickdial page.
Vivaldi is free, user don't need to pay anything. Their revenue model should be very similar to Firefox, Opera, and others, but adding advert to address-bar is a wrong move. Like Ubuntu added Amazon to launcher years ago.