Google Chrome is pretty close. Some extra things I'd like:
* Fully open source, with clear and open licensing.
* Extensions with a permissions system that works at multiple levels of granularity. So I should be able to trust an extension but deny it some specific things (without breaking it.)
* A headless mode, with python/ruby/other bindings, so I can use it as an automation library.
1. I totally agree with the open source part. Although I use a closed source OS often in everyday life (OS X, so at least it's a *nix) I'm a big fan of Linux (which I use on the side, and way before Windows) although personally I like the MIT and BSD type licenses over the (L)GPL
2. Granularity is a great thing to have as well. Extensions could maybe be broken into multiple sections, so you could have a- Permission to inject into page 2- permission to access saved passwords c- permission to access local files etc etc etc, and then you could set its local file root or what sites it can run in.
3. A headless browser sounds pretty great but with the nonstandard essence of web design I wonder how one would use it usefully in automation.
In answer to 3 - ideally in a way similar to http://www.nightmarejs.org/, well worth looking into if you've never played with a headless browser before
* Fully open source, with clear and open licensing.
* Extensions with a permissions system that works at multiple levels of granularity. So I should be able to trust an extension but deny it some specific things (without breaking it.)
* A headless mode, with python/ruby/other bindings, so I can use it as an automation library.