In the past, figuring out how to build Firefox from source tended to be really confusing. The documentation explained too much about how the build system worked, how multiple projects were built, presented too many choices, and generally had lots of details not relevant to most people.
A couple weeks ago, someone on IRC pointed out that jorendorff had created a simplified set of instructions: https://developer.mozilla.org/En/Simple_build I think this is great!
There are still multiple steps (especially if you’re on Windows), but it’s a lot more streamlined than other documentation and is geared towards doing cut’n'paste. In a nutshell, it’s a lot less intimidating.