How can I implement a "web engine" to my project?

Understand "web engine" as an HTML and CSS renderer and JS interpreter, I'm giving preference to Gecko because of my intimacy with Firefox and for knowing that he doesnt open a new process on the machine for each page opened simultaneously, but I'm still open to Webkit and others that I dont know.Anyway, I'm on a project where I need to render and interpret the "web languages". Any tips on where and how to start this integration? Will it cause me a lot of headaches?