diff --git a/mozilla/js/rhino/Makefile b/mozilla/js/rhino/Makefile
index 56dd3c1121b..2177130a36a 100644
--- a/mozilla/js/rhino/Makefile
+++ b/mozilla/js/rhino/Makefile
@@ -74,6 +74,7 @@ helpmessage : FORCE
 	@echo 'Targets include:'
 	@echo '\tall - make jars, examples'
 	@echo '\tjars - make js.jar, jstools.jar'
+	@echo '\tfast - quick-and-dirty "make jars", for development'
 	@echo '\texamples - build the .class files in the examples directory'
 	@echo '\tcheck - perform checks on the source.'
 	@echo '\tclean - remove intermediate files'
@@ -87,12 +88,20 @@ all : jars examples
 
 jars : $(JARS)
 
+fast : fast_$(JS_JAR) $(JSTOOLS_JAR)
+
 # Always call the sub-Makefile - which may decide that the jar is up to date.
 $(JS_JAR) : FORCE
 	$(MAKE) -f $(JS_DIR)/Makefile JAR=$(@) $(EXPORTS) \
 		PATH_PREFIX=$(JS_DIR) \
 		CLASSPATH=.
 
+fast_$(JS_JAR) :
+	$(MAKE) -f $(JS_DIR)/Makefile JAR=$(JS_JAR) $(EXPORTS) \
+		PATH_PREFIX=$(JS_DIR) \
+		CLASSPATH=. \
+		fast
+
 $(JSTOOLS_JAR) : $(JS_JAR) $(JSDEBUG_JAR) FORCE
 	$(MAKE) -f $(JSTOOLS_DIR)/Makefile JAR=$(@) $(EXPORTS) \
 		PATH_PREFIX=$(JSTOOLS_DIR) \
diff --git a/mozilla/js/rhino/org/mozilla/javascript/Makefile b/mozilla/js/rhino/org/mozilla/javascript/Makefile
index 1c20af064b4..fc78f3bd79c 100644
--- a/mozilla/js/rhino/org/mozilla/javascript/Makefile
+++ b/mozilla/js/rhino/org/mozilla/javascript/Makefile
@@ -115,6 +115,10 @@ CLASSES = $(PATH_PREFIX)/*.class $(PATH_PREFIX)/regexp/*.class
 # same thing with RESOURCES.)
 TLCLASS = $(CLASSDIR)/$(PATH_PREFIX)/*.class
 
+# An empty file, used mainly for timestamp/dependency purposes by 
+# "fast" builds
+FASTTARGET=$(CLASSDIR)/.lastbuild
+
 
 $(JAR) : $(TLCLASS) $(CLASSDIR)/$(RESOURCES)
 	cd $(CLASSDIR) ; \
@@ -122,12 +126,32 @@ $(JAR) : $(TLCLASS) $(CLASSDIR)/$(RESOURCES)
 
 $(TLCLASS) : $(SOURCES)
 	- mkdir -p $(CLASSDIR)
+	echo "" > $(FASTTARGET)
 	$(JAVAC) $(JFLAGS) -d $(CLASSDIR) $(SOURCES)
 
 $(CLASSDIR)/$(RESOURCES) : $(RESOURCES)
 	- mkdir -p $(CLASSDIR)/$(RESOURCEDIR)
 	cp $(RESOURCES) $(CLASSDIR)/$(RESOURCEDIR)
 
+# Since the jar file is a target for regular builds, "fast" builds use a 
+# dummy file, updated before each compilation to provide a timestamp.
+# Even so, using a dummy file is far from foolproof, so we still need 
+# the regular build. 
+
+fast: $(FASTTARGET)
+
+# So that we recompile only the files that have changed, we pretend 
+# the only real dependencies are the source files, and recopy the 
+# resources every time.  Right now (14 Jun 99), the only resource is 
+# Messages.properties, so it's a small price to pay.
+$(FASTTARGET) : $(SOURCES)
+	- mkdir -p $(CLASSDIR)/$(RESOURCEDIR)
+	cp $(RESOURCES) $(CLASSDIR)/$(RESOURCEDIR)
+	echo "" > $(FASTTARGET)
+	$(JAVAC) $(JFLAGS) -d $(CLASSDIR) $(?)
+	cd $(CLASSDIR) ; \
+		jar cf ../$(JAR) $(CLASSES) $(RESOURCES)
+
 clean : 
 	- cd $(CLASSDIR) && rm $(CLASSES) $(RESOURCES)
 	- rm $(PATH_PREFIX)/message.ids \