To add to Ocicat's comments...
To my knowledge, this is a rebranded fork of Firefox. Firefox is an extremely complicated application, with hundreds of dependencies on other applications.
You could start with the
www/mozilla-firefox port, and adapt it to meet the requirements of the GNU fork. But ... since you are asking "how to compile" this is a task which I believe is well beyond your skills.
The OpenBSD FAQ includes a
Porter's Handbook, but this assumes the reader has application development or application porting skills.