Why? Because Windows XP and FreeBSD are completely different operating
systems. Their binaries are not compatible.
If you can figure out how to keep the extensions directories separate
while keeping the rest of the preferences the same it should work.
At the worst, you could export your bookmarks from one and import them
into the other. Then you would just have to go through the preferences and
make sure the settings are the same otherwise.
PGP KeyID: 1024D/CBC5D6BB