>  firefox-devel-2.0.0.11-alt1	Provides	pkgconfig(firefox-xpcom) = 2.0.0.11
> +firefox-devel-2.0.0.11-alt1	Requires	/usr/lib/firefox/libgtkembedmoz.so
>  firefox-devel-2.0.0.11-alt1	Requires	/usr/lib/firefox/libmozjs.so
> +firefox-devel-2.0.0.11-alt1	Requires	/usr/lib/firefox/libxpcom.so
>  firefox-devel-2.0.0.11-alt1	Requires	/usr/lib/firefox/libxpcom_core.so

Это зависимости через Libs в *.pc:
/usr/lib/pkgconfig/firefox-gtkmozembed.pc:Libs: -L${libdir} -lgtkembedmoz
/usr/lib/pkgconfig/firefox-xpcom.pc:Libs: -L${libdir} -lxpcom