The generic worker was our first worker that was intended for non-linux environments. In theory it can run against any platform which supports the go programming language, however in practice we use it currently only for Windows™, and the generic worker will be soon superseded by the TaskCluster Worker.
If you are looking at standing up new jobs, we recommend you take a look at the TaskCluster Worker, which is intended to eventually replace the Generic Worker.
For more details on the generic worker, see the reference section.
Building Firefox Desktop for Windows
Please see Building Firefox for Windows™ on Try using TaskCluster for a practical walkthrough of using the Generic Worker for building Firefox Desktop for Windows™.