--- a/calendar/build.mk
+++ b/calendar/build.mk
@@ -66,8 +66,11 @@ endif
 
 endif # COMM_BUILD
 
 installer:
 	@$(MAKE) -C calendar/installer installer
 
 package:
 	@$(MAKE) -C calendar/installer
+
+package-compare:
+	@$(MAKE) -C calendar/installer package-compare

--- a/calendar/installer/Makefile.in
+++ b/calendar/installer/Makefile.in
@@ -90,16 +90,29 @@ ifneq (,$(filter mac cocoa,$(MOZ_WIDGET_
 MOZ_PKG_MAC_DSSTORE=branding/dsstore
 MOZ_PKG_MAC_BACKGROUND=branding/background.png
 MOZ_PKG_MAC_ICON=branding/disk.icns
 MOZ_PKG_MAC_RSRC=branding/license.r
 endif
 
 include $(MOZILLA_SRCDIR)/toolkit/mozapps/installer/packager.mk
 
+ifeq (WINNT,$(OS_ARCH))
+PKGCOMP_FIND_OPTS = 
+else
+PKGCOMP_FIND_OPTS = -L
+endif
+
+package-compare::
+ifdef MOZ_PKG_MANIFEST_P
+	cd $(DIST); find $(PKGCOMP_FIND_OPTS) bin -type f | sort > bin-list.txt
+	grep "^bin" $(MOZ_PKG_MANIFEST) | sed -e 's/\\/\//g' | sort > $(DIST)/pack-list.txt
+	-diff -u $(DIST)/pack-list.txt $(DIST)/bin-list.txt
+endif
+
 installer: removed-files
 ifdef INSTALLER_DIR
 	$(MAKE) -C $(INSTALLER_DIR)
 endif
 
 make-package : removed-files-checked
 
 removed-files-checked : removed-files stage-package