This is basic stuff to anyone who actually maintains a build, but Slashdot hasn't been a forum mostly populated by engineers for a number of years, now.
This appears to be due to link-time optimization blowing up the resident memory size of the linker, taking it past 3GB (which is already a non-standard hack the 32 bit build has had to do). Firefox is large, yes, but this has nothing to do with the final binary - which appears to be about 100MB total including all libraries in the Aurora builds.
I used to routinely run out of 32 bit address space compiling executables for a 64MB embedded ARM platform. This was due to symbol bloat, not executable size (which was 8MB). I also ran out of space compiling for a DSP with 288KB of RAM and 1MB flash, but that was mostly piss poor tools (Tasking). In fact, doesn't Chrome and even the Android sources already require building on a 64 bit host?