I've just tried the build and it fails before that point.
NB when tracing compiler errors you need to get the very first thing that breaks, any output after that point could simply be caused by the first error. (the gecko-mplayer has code to determine the correct utf or UTF to use)
In file included from /usr/include/seamonkey-2.1/plugin/nscore.h:50:0,
/usr/include/seamonkey-2.1/plugin/mozilla/mozalloc.h:109:5: error: expected initializer before 'NS_ATTR_MALLOC'
If I downgrade seamonkey to 2.1b3 (from 13.37) I get a different error from the compiler but it still bombs out.