maybe this patch will help you.

% ldd /usr/local/src/mozilla-1.2.1/mozilla/dist/bin/libnspr4.so
/usr/local/src/mozilla-1.2.1/mozilla/dist/bin/libnspr4.so:
         -lpthread.0 => /usr/lib/libpthread.so.0

--- ../Orig/mozilla/nsprpub/configure.in	2002-09-26 21:46:25.000000000 +0900
+++ ./nsprpub/configure.in	2003-01-31 00:45:26.000000000 +0900
@@ -2127,7 +2127,14 @@
 	        _PTHREAD_LDFLAGS="-lc_r"
 	    fi
 	    ;;
-    *-openbsd*|*-bsdi*|*-netbsd*)
+    *-netbsd*)
+	    AC_DEFINE(_REENTRANT)
+	    AC_DEFINE(_THREAD_SAFE)
+	    if test "$ac_cv_have_dash_pthread" = "yes"; then
+	        _PTHREAD_LDFLAGS="-pthread"
+	    fi
+	    ;;
+    *-openbsd*|*-bsdi*)
 	    AC_DEFINE(_THREAD_SAFE)
 	    dnl -pthread links in -lc_r, so don't specify it explicitly.
 	    if test "$ac_cv_have_dash_pthread" = "yes"; then