> Natural monopoly means that the market only has enough demand for one supplier.

That's not true. Natural monopolies also form due to network effects. You can follow the story of Bell Labs for an early example, which I suspect you're aware of. The reason for a monopoly wasn't for lack of demand it was about tragedy of the commons.

In our modern tech economics we have similar tragedy of the commons but a bit more abstracted. The thing is most products are a result of their userbase, not the product itself. Look at HN. Or look at Reddit or YouTube. It may look like circular logic (because it is a feedback loop), but the fact that everyone is publishing on YouTube makes YouTube bigger and more useful to the consumer which causes more people to publish on that platform because there are more users. It then makes it very difficult to compete because what can you do? You can make a platform that is 100x better than YouTube in respects to serving videos, search, pay to creators, and so on, but you won't win because you have no users and you won't have users without creators who aren't going to produce on your platform because there are no users. In other words, there's a first mover disadvantage. You're an early user and the site sucks because it has no content but you're a true believer. You're an early creator and your pay sucks because there are so few viewers (even if your pay per viewer is 100x your pay per video/time spent is going to be 10000x less because there are 1000000x fewer users). Look at PeerTube, Nebula, or FloatPlane. They are all doing fine but nowhere near as successful as YouTube which everyone hates on (and for good reason). Hell, when YouTube started trying to compete with Twitch they had to REALLY incentivize early creators to move with very lucrative deals because they were not buying the creator, they were buying their userbase. It should be a clear signal that there's an issue if a giant like Google has a hard time competing with Amazon.

For a highly competitive market you need a low barrier to entry so that you can disrupt. There are thousands of examples where a technology/product that is superior in every way (e.g. price and utility) but are not the market winners because network effects exist. Even things like BetaMax vs VHS is a story of network effects (I wouldn't say BetaMax dominated VHS, but not important), because what mattered was what you could get at a store or share (via your neighbor or local rental).

And I'm glad you mention Firefox, because it's a good example of stickiness. I've tried to convert many friends who groan and moan about how hard it is and make up excuses like bookmarks and literally showing them that on startup it'll export for you they just create a new excuse or say UI/UX is trash because the settings button is 3 horizontal lines instead of 3 vertical dots so they can't find it despite being in the same place or tabs are not as curved so its "unusable." You might even see these comments on HN, a place full of tech experts.

What I'm getting at here is that the efficient market hypothesis is clearly false and market participants are clearly not rational (or at least based on the conventional -- economic -- definitions)