Further analysis shows that there are some major changes between Firefox/Fennec 17 and Firefox 24 (the GCC version required is a fair bit higher for a start) so finding out what they installed in Scratchbox (or what build configs and setups were used) for FF/Fennec 17 (or any older versions) doesn't really help.
What I think I need to do is to find the exact minimum requirements (in terms of hardware and software) needed to build Firefox 24.8.1 in a GTK2 build for regular linux and that would probably give me the info needed to ensure I have the right packages for Maemo.
Then for the mozconfig I need to find someone who knows about mozconfig options and GCC flags and things who can help me figure out exactly what I want in a mozconfig based on the defaults for FF24.8.1 as well as what the existing microb-engine configs do.

Figuring out what all the maemo-local patches do and which ones do stuff that is still important (and how to do that same thing in the FF24 codebase) would be a nice thing to do as well but again I dont know the Mozilla codebase well enough for that