Are there any modern X11/Xorg Browsers that compile for OSX? Currently I'm using macports. I'm wondering if there are any graphical X11 browsers like Chromium, or Firefox, or the like that compile under X11 (and not native OSX). I want a browser that I can manage with an X11 Desktop Environment (like i3).

My criteria would be modern (executes javascript), graphical, and maintained. I know there are other build systems out there like Fink, and even more projects that aren't available under Fink or Macports so I'm willing to cast a wide net to find something.

Chromium would be great.

I see some threads where people have asked similar questions but most of these are at least 4 years old.
I'm not sure your reason for wanting a browser under X11, but your needs might be met by running Chromium or Firefox in a Docker container over VNC. Then, you can use any window manager you want.

For example, here's my container that exposes Firefox through OpenBox. 

Firefox over VNC on Docker Hub