Linux - boot in runlevel3 and add X11 components

I want to build a minimum Linux for embedded devices that comes with Firefox only.

Questions:

1. Is it ever possible to add X11 components to runlevel3 and upgrade it to runlevel5?
2. Is it possible to setup a Linux in runlevel3 with minimum display support so that I be able to run Firefox? (Not interested in text based browsers)

I gave it a go but I got lots of dependency errors trying to install X11-common with apt-get in runlevel3.

Linux From Scratch is a step-by-step instruction book for anyone who wants to gain a good understanding of how to build own custom Linux distro.

1. There is a dedicated topic about X Window System Environment

This includes the base LFS project and a bunch of extensions derived from it. For embedded systems Cross Linux From Scratch is of particular interest.

Another option - in case you want to do it faster but losing deep understanding - is using some Embedded Linux distro builder like Buildroot