While I don't mind coding with JavaScript, I'd much rather use the language of my choice both within the browser and in server-side code.
There exist dozens of languages and language enhancements designed to be compiled to JavaScript for running within a browser. While performance may be acceptable with modern browsers, the developer experience is still far from perfect: The debugger doesn't let you step through your original source and the languages available are limited.
If browsers were to build in a language runtime, such as a CLR, the choice of 'native' browser languages would expand greatly - and include languages such as : Java, C#, Python, Ruby, Haskell, Scala, Erlang and OCaml/F#. JavaScript would be supported on the same runtime of course!
An interesting 'feature' would be that tools like .NET Reflector could be developed to 'decompile' VM bytecode found in any page back to whatever language the developer preferred. Of course this wouldn't be perfect, but if you're used to working with C# and the original code was written in Scala, you would likely find that the decompiled version looked similar enough for you to work with it.
I'm leaning towards preferring a CLR rather than a JVM, as what I've read suggests that it's easier to get Java (the language) and JVM code (via IKVM) working on a CLR than C# and .NET code working on a JVM.