During GRE I lead the charge to restructure the codebase for a multitude of reasons. Though less respectable ones no longer apply the more legit ones still do.
The following are considered hot paths for patching and will not be moved/broken up any time soon:
The following will stay at topsrcdir regardless:
The following are hubs where the majority of things live:
Going forward libs will be in third_party. Top level components and modules that we consider ours pretty much will go to a sub-directory of runtime while system will retain complex moztrees with their original names so that when porting to these complex trees and hotpaths I can just remove the prepending slash.
Opening Post will be updated soonish.