Start out with a solid base: (for example)
- https://cefbuilds.com/
- https://crosswalk-project.org/
- http://electron.atom.io/
- http://nwjs.io/
or you try to help with existing projects: (for example)
- https://github.com/breach/thrust (started out with https://github.com/breach/breach_core a "javascript"-Browser (core is not js))
https://github.com/minbrowser/min
easy bugs to hunt: https://github.com/servo/servo/labels/E-easy