When building the repo locally after setting up everything properly I get a message that the flash browser is no longer supported due to Flash being disabled as of last year. Is there any documentation that can help me build this locally properly?

This code is probably too old to be compiled with newer versions of Haxe, although mentions of Flash are weird anyway. Just in case: you need to build for html, so your command should be "openfl test html5" or something like that. I'll try to check it when I have time.