A Web browser is a complex piece of SW that needs to provide many, many, features and work with great performance. Therefore you need a large team of experienced developers (full-time and maybe volunteers) collaborating on the development and testing. This is cost in labor a d infrastructures (servers, storage, Internet connection, hosting of platforms, etc)

One such feature that is a must-have is playing videos, from YouTube, Netflix, Prime, Twitch and what have you. Most widely spread video codecs are proprietary, you need a license to implement the decoder and these licenses are expensive. H.264 is one such codec, very widely spread across many content and platforms. You wouldn’t want a Web browser that lacks the ability to decide H.264 videos. There are many such codecs that are considered essential, and this cost a lot of money in total.

In conclusion, is an argument as why developing a web browser costs money and requires a sustainable financial plan to persist, even though it is open-source and developed mostly by volunteers.

My personal opinion: advertisement sucks. I don’t want it anywhere in my life. I would prefer to pay upfront for my web browser if it come to this.