Java has only single dominant JVM, but in several flavours. It is doing fine.
JVM has many competing implementations[1]. Also it is not used by clueless end users, but by tech workers. They will protest is JVM gets "phone home" "features" and other bloatware privacy-killing crap.
End users of browsers do not have this insight into their tools.
Yes, Oracle's JVM is dominant (but not on Android, which is a huge installed base). So is Chrome in browser land. Still good that Java has many, and FF exists.
[1]: https://en.wikipedia.org/wiki/List_of_Java_virtual_machines
I hear this argument, and it makes sense...
But a lot of us still pucker up if you mention the word "IE6" and we never want to risk going down that path again. :)
There's a balance between diversity and monopoly that can be struck.
Really? I prefer there are a few, but mostly compatible techs in that space. This is the VM that runs almost all desktop (client) software these days. Having only one implementation would IMHO be a disaster.