diff -Naur comm-release.orig/config/rules.mk comm-release/config/rules.mk
--- comm-release.orig/config/rules.mk	2012-06-05 07:50:26.000000000 +0200
+++ comm-release/config/rules.mk	2012-06-06 13:47:38.584972657 +0200
@@ -1518,7 +1518,7 @@
 	$(PYTHON) -u $(MOZILLA_DIR)/config/pythonpath.py \
 	  -I$(MOZILLA_DIR)/other-licenses/ply \
 	  -I$(MOZILLA_DIR)/xpcom/idl-parser \
-	  $(MOZILLA_DIR)/xpcom/idl-parser/header.py --cachedir=$(MOZILLA_DIR)/xpcom/idl-parser $(XPIDL_FLAGS) $(_VPATH_SRCS) -d $(MDDEPDIR)/$(@F).pp -o $@
+	  $(MOZILLA_DIR)/xpcom/idl-parser/header.py --cachedir=$(MOZILLA_DIR)/xpcom/idl-parser/cache $(XPIDL_FLAGS) $(_VPATH_SRCS) -d $(MDDEPDIR)/$(@F).pp -o $@
 	@if test -n "$(findstring $*.h, $(EXPORTS))"; \
 	  then echo "*** WARNING: file $*.h generated from $*.idl overrides $(srcdir)/$*.h"; else true; fi
 
@@ -1531,7 +1531,7 @@
 	  -I$(MOZILLA_DIR)/other-licenses/ply \
 	  -I$(MOZILLA_DIR)/xpcom/idl-parser \
 	  -I$(MOZILLA_DIR)/xpcom/typelib/xpt/tools \
-	  $(MOZILLA_DIR)/xpcom/idl-parser/typelib.py --cachedir=$(MOZILLA_DIR)/xpcom/idl-parser $(XPIDL_FLAGS) $(_VPATH_SRCS) -d $(MDDEPDIR)/$(@F).pp -o $@
+	  $(MOZILLA_DIR)/xpcom/idl-parser/typelib.py --cachedir=$(MOZILLA_DIR)/xpcom/idl-parser/cache $(XPIDL_FLAGS) $(_VPATH_SRCS) -d $(MDDEPDIR)/$(@F).pp -o $@
 
 # no need to link together if XPIDLSRCS contains only XPIDL_MODULE
 ifneq ($(XPIDL_MODULE).idl,$(strip $(XPIDLSRCS)))
diff -Naur comm-release.orig/mozilla/config/rules.mk comm-release/mozilla/config/rules.mk
--- comm-release.orig/mozilla/config/rules.mk	2012-06-05 07:54:07.000000000 +0200
+++ comm-release/mozilla/config/rules.mk	2012-06-06 13:47:38.585972872 +0200
@@ -1479,7 +1479,7 @@
 	$(PYTHON_PATH) \
 	  -I$(topsrcdir)/other-licenses/ply \
 	  -I$(topsrcdir)/xpcom/idl-parser \
-	  $(topsrcdir)/xpcom/idl-parser/header.py --cachedir=$(DEPTH)/xpcom/idl-parser $(XPIDL_FLAGS) $(_VPATH_SRCS) -d $(MDDEPDIR)/$(@F).pp -o $@
+	  $(topsrcdir)/xpcom/idl-parser/header.py --cachedir=$(DEPTH)/xpcom/idl-parser/cache $(XPIDL_FLAGS) $(_VPATH_SRCS) -d $(MDDEPDIR)/$(@F).pp -o $@
 	@if test -n "$(findstring $*.h, $(EXPORTS))"; \
 	  then echo "*** WARNING: file $*.h generated from $*.idl overrides $(srcdir)/$*.h"; else true; fi
 
@@ -1492,7 +1492,7 @@
 	  -I$(topsrcdir)/other-licenses/ply \
 	  -I$(topsrcdir)/xpcom/idl-parser \
 	  -I$(topsrcdir)/xpcom/typelib/xpt/tools \
-	  $(topsrcdir)/xpcom/idl-parser/typelib.py --cachedir=$(DEPTH)/xpcom/idl-parser $(XPIDL_FLAGS) $(_VPATH_SRCS) -d $(MDDEPDIR)/$(@F).pp -o $@
+	  $(topsrcdir)/xpcom/idl-parser/typelib.py --cachedir=$(DEPTH)/xpcom/idl-parser/cache $(XPIDL_FLAGS) $(_VPATH_SRCS) -d $(MDDEPDIR)/$(@F).pp -o $@
 
 # no need to link together if XPIDLSRCS contains only XPIDL_MODULE
 ifneq ($(XPIDL_MODULE).idl,$(strip $(XPIDLSRCS)))
diff -Naur comm-release.orig/mozilla/js/src/config/rules.mk comm-release/mozilla/js/src/config/rules.mk
--- comm-release.orig/mozilla/js/src/config/rules.mk	2012-06-05 07:54:14.000000000 +0200
+++ comm-release/mozilla/js/src/config/rules.mk	2012-06-06 13:47:38.648984016 +0200
@@ -1479,7 +1479,7 @@
 	$(PYTHON_PATH) \
 	  -I$(topsrcdir)/other-licenses/ply \
 	  -I$(topsrcdir)/xpcom/idl-parser \
-	  $(topsrcdir)/xpcom/idl-parser/header.py --cachedir=$(DEPTH)/xpcom/idl-parser $(XPIDL_FLAGS) $(_VPATH_SRCS) -d $(MDDEPDIR)/$(@F).pp -o $@
+	  $(topsrcdir)/xpcom/idl-parser/header.py --cachedir=$(DEPTH)/xpcom/idl-parser/cache $(XPIDL_FLAGS) $(_VPATH_SRCS) -d $(MDDEPDIR)/$(@F).pp -o $@
 	@if test -n "$(findstring $*.h, $(EXPORTS))"; \
 	  then echo "*** WARNING: file $*.h generated from $*.idl overrides $(srcdir)/$*.h"; else true; fi
 
@@ -1492,7 +1492,7 @@
 	  -I$(topsrcdir)/other-licenses/ply \
 	  -I$(topsrcdir)/xpcom/idl-parser \
 	  -I$(topsrcdir)/xpcom/typelib/xpt/tools \
-	  $(topsrcdir)/xpcom/idl-parser/typelib.py --cachedir=$(DEPTH)/xpcom/idl-parser $(XPIDL_FLAGS) $(_VPATH_SRCS) -d $(MDDEPDIR)/$(@F).pp -o $@
+	  $(topsrcdir)/xpcom/idl-parser/typelib.py --cachedir=$(DEPTH)/xpcom/idl-parser/cache $(XPIDL_FLAGS) $(_VPATH_SRCS) -d $(MDDEPDIR)/$(@F).pp -o $@
 
 # no need to link together if XPIDLSRCS contains only XPIDL_MODULE
 ifneq ($(XPIDL_MODULE).idl,$(strip $(XPIDLSRCS)))
diff -Naur comm-release.orig/mozilla/js/xpconnect/src/Makefile.in comm-release/mozilla/js/xpconnect/src/Makefile.in
--- comm-release.orig/mozilla/js/xpconnect/src/Makefile.in	2012-06-05 07:54:16.000000000 +0200
+++ comm-release/mozilla/js/xpconnect/src/Makefile.in	2012-06-06 13:51:37.351993078 +0200
@@ -151,7 +151,7 @@
 	  -I$(topsrcdir)/xpcom/idl-parser \
 	  $(srcdir)/qsgen.py \
 	  --idlpath=$(DEPTH)/dist/idl \
-	  --cachedir=$(DEPTH)/xpcom/idl-parser \
+	  --cachedir=$(DEPTH)/xpcom/idl-parser/cache \
 	  --header-output dom_quickstubs.h \
 	  --stub-output dom_quickstubs.cpp \
 	  --makedepend-output $(MDDEPDIR)/dom_qsgen.pp \
@@ -172,7 +172,7 @@
 	  -I$(topsrcdir)/xpcom/idl-parser \
 	  $(srcdir)/dombindingsgen.py \
 	  --idlpath=$(DEPTH)/dist/idl \
-	  --cachedir=$(DEPTH)/xpcom/idl-parser \
+	  --cachedir=$(DEPTH)/xpcom/idl-parser/cache \
 	  --header-output dombindings_gen.h \
 	  $(srcdir)/dombindings.conf
 
@@ -189,7 +189,7 @@
 	  -I$(topsrcdir)/xpcom/idl-parser \
 	  $(srcdir)/dombindingsgen.py \
 	  --idlpath=$(DEPTH)/dist/idl \
-	  --cachedir=$(DEPTH)/xpcom/idl-parser \
+	  --cachedir=$(DEPTH)/xpcom/idl-parser/cache \
 	  --stub-output dombindings_gen.cpp \
 	  --makedepend-output $(MDDEPDIR)/dombindingsgen.pp \
 	  $(srcdir)/dombindings.conf
@@ -208,7 +208,7 @@
 	  -I$(topsrcdir)/xpcom/idl-parser \
 	  $(srcdir)/dictionary_helper_gen.py \
 	  -I $(DEPTH)/dist/idl \
-	  --cachedir=$(DEPTH)/xpcom/idl-parser \
+	  --cachedir=$(DEPTH)/xpcom/idl-parser/cache \
 	  --header-output DictionaryHelpers.h \
 	  $(srcdir)/dictionary_helper_gen.conf
 
@@ -223,7 +223,7 @@
 	  -I$(topsrcdir)/xpcom/idl-parser \
 	  $(srcdir)/dictionary_helper_gen.py \
 	  -I $(DEPTH)/dist/idl \
-	  --cachedir=$(DEPTH)/xpcom/idl-parser \
+	  --cachedir=$(DEPTH)/xpcom/idl-parser/cache \
 	  --header-output DictionaryHelpers.h \
 	  --stub-output DictionaryHelpers.cpp \
 	  --makedepend-output $(MDDEPDIR)/dictionary_helper_gen.pp \
diff -Naur comm-release.orig/mozilla/xpcom/idl-parser/Makefile.in comm-release/mozilla/xpcom/idl-parser/Makefile.in
--- comm-release.orig/mozilla/xpcom/idl-parser/Makefile.in	2012-06-05 07:54:27.000000000 +0200
+++ comm-release/mozilla/xpcom/idl-parser/Makefile.in	2012-06-06 13:47:38.650984513 +0200
@@ -61,7 +61,7 @@
 	$(PYTHON_PATH) \
 	  -I$(topsrcdir)/other-licenses/ply \
 	  -I$(topsrcdir)/xpcom/idl-parser \
-	  $(topsrcdir)/xpcom/idl-parser/header.py --cachedir=. --regen
+	  $(topsrcdir)/xpcom/idl-parser/header.py --cachedir=$(DEPTH)/xpcom/idl-parser/cache --regen
 
 check::
 	$(PYTHON_PATH) \
diff -Naur comm-release.orig/mozilla/xpcom/typelib/xpidl/Makefile.in comm-release/mozilla/xpcom/typelib/xpidl/Makefile.in
--- comm-release.orig/mozilla/xpcom/typelib/xpidl/Makefile.in	2012-06-05 07:54:27.000000000 +0200
+++ comm-release/mozilla/xpcom/typelib/xpidl/Makefile.in	2012-06-06 13:47:38.650984513 +0200
@@ -48,8 +48,8 @@
   $(topsrcdir)/xpcom/idl-parser/xpidl.py \
   $(topsrcdir)/xpcom/idl-parser/header.py \
   $(topsrcdir)/xpcom/idl-parser/typelib.py \
-  $(DEPTH)/xpcom/idl-parser/xpidllex.py \
-  $(DEPTH)/xpcom/idl-parser/xpidlyacc.py \
+  $(DEPTH)/xpcom/idl-parser/cache/xpidllex.py \
+  $(DEPTH)/xpcom/idl-parser/cache/xpidlyacc.py \
   $(NULL)
 
 ifndef MOZ_SYSTEM_PLY