My solution for a few "bugs considered features" in huge open-source software like Firefox was to just patch the binary. Much easier than figuring out how to build it, and with only the change I wanted.
Yes, several decades of experience. Mainly Windbg now but I used to use SoftICE a lot. Look for error (or otherwise) messages/codes and use breakpoints to guide your exploration. Of course, the source code is also available, but sometimes it's even more difficult to follow than the binary if what you're looking for is obfuscated in several layers of compiled-out indirections.
