Being open source is a red herring in this instance.

Say that Chrome implements a web feature you don't like. You fork the browser and remove that feature. But websites expect Chrome, and they use that feature, so your fork doesn't work with those websites.

Say that Chrome refuses to add a feature you want. You fork the browser and add the feature. But websites expect Chrome, so they don't use your feature so as to not break for their Chrome users, and your fork is no better off.

The insidious part of a web monoculture is allowing Google to dictate the standards of the web platform. Being able to fork the codebase only gives one the power to change things that are strictly client-side.

Using the same engine across multiple browsers, open source or not, just doesn’t cut it.

Mozilla is Poland and is destined to get f*cked as their market share drops and any negotiating leverage they have to get Google TAC money disappears (they're more like Saudi Arabia is to the US, a vassal state, rather than a Great Power).

These are dire times for the web. Only Vestager can save us now.

[1] https://en.wikipedia.org/wiki/European_balance_of_power

[2] https://stratechery.com/2018/the-end-of-windows/

Sometimes innovation is at odds with whatever Google's Chrome team feels like doing. That is why engine diversity is a good thing.

- Without competitors, innovation is dead. If there was only one web-engine, why bother improving it further? Given that it's open-source, it could theoretically be forked, but in that moment you again have two different web engines or more. Also, Mozilla would have to fork Blink from day one, because many things in it, they do not consider acceptable.

- A monoculture means one security problem makes everyone vulnerable.

- Multiple implementations challenge standards. You still would want a definition of a standard, or an API if you will, to point web developers to. But those are only going to point problems out after you've already implemented it, and likely also after other websites are already using the feature productively. They also can't point out stupid specifications that aren't going to allow you to update your browser engine in the future. So, you'd be much more likely to have to break compatibility, which doesn't play well with the web.

Not that I know that well, my work that forces my Windows usage still makes me use IE.

So, as the OP said - back to the bad old days of IE6 dominance.