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)