diff --git a/xpinstall/public/nsISoftwareUpdate.h b/xpinstall/public/nsISoftwareUpdate.h
index 3cdb0f79ba6..6507d231c34 100644
--- a/xpinstall/public/nsISoftwareUpdate.h
+++ b/xpinstall/public/nsISoftwareUpdate.h
@@ -65,10 +65,10 @@
 #define XPI_NO_NEW_THREAD   0x1000
 
 #define NS_ISOFTWAREUPDATE_IID                   \
-{ 0x18c2f992, 									 \
-  0xb09f, 										 \
-  0x11d2,						                 \
- {0xbc, 0xde, 0x00, 0x80, 0x5f, 0x0e, 0x13, 0x53}\
+{ 0xfc7c086f,                                    \
+  0xdae0,                                        \
+  0x45e0,                                        \
+ {0x99, 0x10, 0xd5, 0xda, 0x91, 0xc8, 0x27, 0x46}\
 }
 
 class nsIPrincipal;
@@ -95,7 +95,7 @@ class nsISoftwareUpdate : public nsISupports
             NS_IMETHOD RegisterListener(nsIXPIListener *aListener) = 0;
 
             /* FIX: these should be in a private interface */
-            NS_IMETHOD InstallJarCallBack()                   = 0;
+            NS_IMETHOD_(void) InstallJarCallBack() = 0;
             NS_IMETHOD GetMasterListener(nsIXPIListener **aListener) = 0;
             NS_IMETHOD SetActiveListener(nsIXPIListener *aListener) = 0;
 };
diff --git a/xpinstall/src/nsSoftwareUpdate.cpp b/xpinstall/src/nsSoftwareUpdate.cpp
index aabe0b03dde..0590660f250 100644
--- a/xpinstall/src/nsSoftwareUpdate.cpp
+++ b/xpinstall/src/nsSoftwareUpdate.cpp
@@ -358,7 +358,7 @@ nsSoftwareUpdate::InstallChrome( PRUint32 aType,
 }
 
 
-NS_IMETHODIMP
+NS_IMETHODIMP_(void)
 nsSoftwareUpdate::InstallJarCallBack()
 {
     PR_Lock(mLock);
@@ -375,7 +375,7 @@ nsSoftwareUpdate::InstallJarCallBack()
 
     PR_Unlock(mLock);
 
-    return RunNextInstall();
+    RunNextInstall();
 }
 
 
diff --git a/xpinstall/src/nsSoftwareUpdate.h b/xpinstall/src/nsSoftwareUpdate.h
index 9cef0c49641..e62a6a870ca 100644
--- a/xpinstall/src/nsSoftwareUpdate.h
+++ b/xpinstall/src/nsSoftwareUpdate.h
@@ -66,7 +66,7 @@ class nsSoftwareUpdate: public nsISoftwareUpdate,
 
         NS_IMETHOD RegisterListener(nsIXPIListener *aListener);
 
-        NS_IMETHOD InstallJarCallBack();
+        NS_IMETHOD_(void) InstallJarCallBack();
         NS_IMETHOD GetMasterListener(nsIXPIListener **aListener);
         NS_IMETHOD SetActiveListener(nsIXPIListener *aListener);
 
diff --git a/xpinstall/src/nsSoftwareUpdateRun.cpp b/xpinstall/src/nsSoftwareUpdateRun.cpp
index 6a3aa3b5dbb..e45976b30ee 100644
--- a/xpinstall/src/nsSoftwareUpdateRun.cpp
+++ b/xpinstall/src/nsSoftwareUpdateRun.cpp
@@ -582,7 +582,19 @@ extern "C" void PR_CALLBACK RunInstallOnThread(void *data)
     if (scriptBuffer) delete [] scriptBuffer;
 
     softwareUpdate->SetActiveListener(0);
-    softwareUpdate->InstallJarCallBack();
+    
+    if (installInfo->GetFlags() & XPI_NO_NEW_THREAD)
+    {
+        softwareUpdate->InstallJarCallBack();
+    }
+    else
+    {
+        // Proxy the callback to the main thread
+        nsCOMPtr<nsIRunnable> callback = NS_NEW_RUNNABLE_METHOD(nsISoftwareUpdate,
+                                                                softwareUpdate,
+                                                                InstallJarCallBack);
+        NS_DispatchToMainThread(callback);
+    }
 }