152651 Main menu items get forver disabled after the invocation of Save File dialog.

r=jag, sr=bz
Check in for Simford.Dong@sun.com's fix

suite/browser/nsBrowserStatusHandler.js

@@ -82,6 +82,8 @@ nsBrowserStatusHandler.prototype =
 
   hideAboutBlank : true,
 
+  locationChanged : false,  
+
   QueryInterface : function(aIID)
   {
     if (aIID.equals(Components.interfaces.nsIWebProgressListener) ||
@@ -225,6 +227,8 @@ nsBrowserStatusHandler.prototype =
         this.stopButton.disabled = false;
         this.stopMenu.removeAttribute('disabled');
         this.stopContext.removeAttribute('disabled');
+
+        this.locationChanged = false;        
       }
     }
     else if (aStateFlags & nsIWebProgressListener.STATE_STOP) {
@@ -273,7 +277,12 @@ nsBrowserStatusHandler.prototype =
           }
           this.status = "";
           this.setDefaultStatus(msg);
-          if (channel) {
+          
+          //if the location hasn't been changed, the document may be null(eg a full-page plugin),
+          //we may not be able to get the correct content-type. 
+          //so we need to skip the test and keep the menu status.
+          //otherwise(this.locationChanged = true), test normally.
+          if (channel && this.locationChanged) {
             try {
               ctype = channel.contentType;
               if (this.mimeTypeIsTextBased(ctype))
@@ -336,6 +345,8 @@ nsBrowserStatusHandler.prototype =
       SetPageProxyState("valid", aLocation);
     }
     UpdateBackForwardButtons();
+
+    this.locationChanged = true;    
   },
 
   onStatusChange : function(aWebProgress, aRequest, aStatus, aMessage)