hey andy (hope that's an acceptable short version of your name as well ).
That's a good and hard to anwser question. Well, we had some time ago a guy working full-time on compile options for code reduction, and we reliazed that it wouldn't be a piece of cake getting significant reduction through this path.
But if you check the your target_dir/ (after 'make install') after building minimo, you'll notice some directories not relevant for us (they are for minimo, not for manaos), like ____'chrome' [sbox-meamo: /usr/lib/mozilla-manaos-engine] > du -sh chrome/ 3.0M chrome ____'res' - it could be also removed out (at least partially) [sbox-meamo: /usr/lib/mozilla-manaos-engine] > du -s res/ 928 res , isn't it a good start point ?! I got 4 mb easily.
We are working on the mozconfig file as well. I hope to get 11 mb before the end of this year ! that's what I can say for instance ... What do you think ?