diff --git a/xpcom/build/Makefile.in b/xpcom/build/Makefile.in

--- a/xpcom/build/Makefile.in

+++ b/xpcom/build/Makefile.in

@@ -161,17 +161,18 @@ OS_LIBS += $(LIBICONV)

 GARBAGE         += $(XPCOM_GLUE_SRC_LCSRCS) $(XPCOM_GLUE_SRC_LCPPSRCS) $(XPCOM_GLUENS_SRC_LCPPSRCS) $(wildcard *.$(OBJ_SUFFIX))

 include $(topsrcdir)/config/rules.mk

 DEFINES		+= \

 		-D_IMPL_NS_COM \

 		-D_IMPL_NS_STRINGAPI \

 		-DEXPORT_XPT_API \

-		-DEXPORT_XPTC_API

+		-DEXPORT_XPTC_API \

+		-DMOZ_WIDGET_TOOLKIT=\"$(MOZ_WIDGET_TOOLKIT)\"

 EXTRA_DSO_LDOPTS += $(NSPR_LIBS)

 ifdef GC_LEAK_DETECTOR

 DEFINES += -DGC_LEAK_DETECTOR

 endif

 ifdef TARGET_XPCOM_ABI

diff --git a/xpcom/glue/Makefile.in b/xpcom/glue/Makefile.in

--- a/xpcom/glue/Makefile.in

+++ b/xpcom/glue/Makefile.in

@@ -157,11 +157,13 @@ include $(topsrcdir)/config/rules.mk

 ifdef _MSC_VER

 # Don't include directives about which CRT to use

 OS_COMPILE_CXXFLAGS += -Zl

 OS_COMPILE_CFLAGS += -Zl

 DEFINES += -D_USE_ANSI_CPP

 endif

+DEFINES += -DMOZ_WIDGET_TOOLKIT=\"$(MOZ_WIDGET_TOOLKIT)\"

+

 ifdef TARGET_XPCOM_ABI

 DEFINES += -DTARGET_XPCOM_ABI=\"$(TARGET_XPCOM_ABI)\"

 endif

diff --git a/xpcom/glue/nsGREGlue.cpp b/xpcom/glue/nsGREGlue.cpp

--- a/xpcom/glue/nsGREGlue.cpp

+++ b/xpcom/glue/nsGREGlue.cpp

@@ -157,36 +157,46 @@ GRE_GetPathFromRegKey(HKEY aRegKey,

 nsresult

 GRE_GetGREPathWithProperties(const GREVersionRange *versions,

                              PRUint32 versionsLength,

                              const GREProperty *properties,

                              PRUint32 propertiesLength,

                              char *aBuffer, PRUint32 aBufLen)

 {

+  // append the widget information to be able to have multiple xulrunners

+  // based on different widget toolkits installed

+  static const GREProperty kWidgetProperty =

+    { "widget", MOZ_WIDGET_TOOLKIT };

+

 #ifdef TARGET_XPCOM_ABI

-  // append the ABI to the properties to match only binary 

+  // append the ABI to the properties to match only binary

   // compatible GREs

-  static const GREProperty kExtraProperty =

-    { "abi", TARGET_XPCOM_ABI };

+  static const GREProperty kAbiProperty =

+  { "abi", TARGET_XPCOM_ABI };

+  GREProperty *allProperties = new GREProperty[propertiesLength + 2];

+#else

   GREProperty *allProperties = new GREProperty[propertiesLength + 1];

+#endif

   if (!allProperties)

     return NS_ERROR_OUT_OF_MEMORY;

   for (PRUint32 i=0; i<propertiesLength; i++) {

     allProperties[i].property = properties[i].property;

     allProperties[i].value    = properties[i].value;

   }

-  allProperties[propertiesLength].property = kExtraProperty.property;

-  allProperties[propertiesLength].value    = kExtraProperty.value;

+  allProperties[propertiesLength].property = kWidgetProperty.property;

+  allProperties[propertiesLength].value    = kWidgetProperty.value;

+#ifdef TARGET_XPCOM_ABI

+  allProperties[propertiesLength+1].property = kAbiProperty.property;

+  allProperties[propertiesLength+1].value    = kAbiProperty.value;

+  PRUint32 allPropertiesLength = propertiesLength + 2;

+#else

   PRUint32 allPropertiesLength = propertiesLength + 1;

-#else

-  const GREProperty *allProperties = properties;

-  PRUint32 allPropertiesLength = propertiesLength;

 #endif

   // if GRE_HOME is in the environment, use that GRE

   const char* env = getenv("GRE_HOME");

   if (env && *env) {

     char p[MAXPATHLEN];

     snprintf(p, sizeof(p), "%s" XPCOM_FILE_PATH_SEPARATOR XPCOM_DLL, env);

     p[sizeof(p) - 1] = '\0';

diff --git a/xpcom/glue/standalone/Makefile.in b/xpcom/glue/standalone/Makefile.in

--- a/xpcom/glue/standalone/Makefile.in

+++ b/xpcom/glue/standalone/Makefile.in

@@ -120,14 +120,15 @@ OS_COMPILE_CFLAGS += -Zl

 DEFINES += -D_USE_ANSI_CPP

 endif

 export:: $(XPCOM_GLUE_SRC_CSRCS) $(XPCOM_GLUE_SRC_CPPSRCS) $(topsrcdir)/xpcom/glue/nsStringAPI.cpp

 	$(INSTALL) $^ .

 GARBAGE += nsStringAPI.cpp

-DEFINES		+= -DXPCOM_GLUE

+DEFINES		+= -DXPCOM_GLUE \

+                   -DMOZ_WIDGET_TOOLKIT=\"$(MOZ_WIDGET_TOOLKIT)\"

 ifdef TARGET_XPCOM_ABI

 DEFINES += -DTARGET_XPCOM_ABI=\"$(TARGET_XPCOM_ABI)\"

 endif

diff --git a/xulrunner/app/Makefile.in b/xulrunner/app/Makefile.in

--- a/xulrunner/app/Makefile.in

+++ b/xulrunner/app/Makefile.in

@@ -59,17 +59,18 @@ PROGRAM = xulrunner$(BIN_SUFFIX)

 else

 ifeq ($(OS_ARCH), BeOS)

 PROGRAM = xulrunner$(BIN_SUFFIX)

 else

 PROGRAM = xulrunner-bin$(BIN_SUFFIX)

 endif

 endif

-DEFINES += -DXULRUNNER_PROGNAME=\"xulrunner\"

+DEFINES += -DXULRUNNER_PROGNAME=\"xulrunner\" \

+           -DMOZ_WIDGET_TOOLKIT=\"$(MOZ_WIDGET_TOOLKIT)\"

 ifdef MOZ_JAVAXPCOM

 DEFINES += -DMOZ_JAVAXPCOM

 endif

 ifdef TARGET_XPCOM_ABI

 DEFINES += -DTARGET_XPCOM_ABI=\"$(TARGET_XPCOM_ABI)\"

 endif

diff --git a/xulrunner/app/nsXULRunnerApp.cpp b/xulrunner/app/nsXULRunnerApp.cpp

--- a/xulrunner/app/nsXULRunnerApp.cpp

+++ b/xulrunner/app/nsXULRunnerApp.cpp

@@ -257,17 +257,18 @@ InstallXULApp(nsIFile* aXULRunnerDir,

   if (NS_FAILED(rv))

     return 3;

   return 0;

 }

 static const GREProperty kGREProperties[] = {

-  { "xulrunner", "true" }

+  { "xulrunner", "true" },

+  { "widget", MOZ_WIDGET_TOOLKIT }

 #ifdef TARGET_XPCOM_ABI

   , { "abi", TARGET_XPCOM_ABI }

 #endif

 #ifdef MOZ_JAVAXPCOM

   , { "javaxpcom", "1" }

 #endif

 };

diff --git a/xulrunner/installer/Makefile.in b/xulrunner/installer/Makefile.in

--- a/xulrunner/installer/Makefile.in

+++ b/xulrunner/installer/Makefile.in

@@ -63,18 +63,18 @@ endif

 include $(topsrcdir)/config/rules.mk

 INSTALL_SDK = 1

 include $(topsrcdir)/toolkit/mozapps/installer/packager.mk

 $(MOZILLA_VERSION).system.conf: $(topsrcdir)/config/milestone.txt Makefile

-	printf "[%s]\nGRE_PATH=%s\nxulrunner=true\nabi=%s" \

-	  $(MOZILLA_VERSION) $(installdir) $(TARGET_XPCOM_ABI)> $@

+	printf "[%s]\nGRE_PATH=%s\nxulrunner=true\nwidget=%s\nabi=%s" \

+	  $(MOZILLA_VERSION) $(installdir) $(MOZ_WIDGET_TOOLKIT) $(TARGET_XPCOM_ABI)> $@

 ifndef SKIP_GRE_REGISTRATION

 # to register xulrunner per-user, override this with $HOME/.gre.d

 regdir = /etc/gre.d

 install:: $(MOZILLA_VERSION).system.conf

 	$(NSINSTALL) -D $(DESTDIR)$(regdir)

 	$(SYSINSTALL) $(IFLAGS1) $^ $(DESTDIR)$(regdir)