81061 - implement folder deletion in history.

73927 - use batch deleting for history (a speedup of 30000% for a few hundred items!).

63292 - session additions to global history are lost on a crash.

112308 - 2M history.dat file adds 30% to startup time.

96753 - changing history grouping doesn't update open sidebar panels.

98776 - support context menus on folders in global history.

124665 - can't clear global history after startup if you don't have a homepage.

93233 - with large history, clear history appears to hang.

92613 - shouldn't store chrome uris in global history.

59816 - clear history button should be disabled if history is empty; add count attr to nsIBrowserHistory.

104231 - last typed web location remains after clearing all history.

r=ben sr=alecf

suite/common/pref/pref-history.xul

@@ -39,15 +39,26 @@
   { 
     parent.hPrefWindow.registerOKCallbackFunc(onHistoryOK);
 
-    var button = document.getElementById("ClearUrlBarHistoryButton");
+    var urlbarHistButton = document.getElementById("ClearUrlBarHistoryButton");
     try {
       var urlBarHist = Components.classes["@mozilla.org/browser/urlbarhistory;1"]
                                  .getService(Components.interfaces.nsIUrlbarHistory);
-      var isBtnLocked = parent.hPrefWindow.getPrefIsLocked(button.getAttribute("prefstring"));
-      button.disabled = ( urlBarHist.count == 0 ) || isBtnLocked ;
+      var isBtnLocked = parent.hPrefWindow.getPrefIsLocked(urlbarHistButton.getAttribute("prefstring"));
+      var pref = Components.classes["@mozilla.org/preferences-service;1"]
+                           .getService(Components.interfaces.nsIPrefBranch);
+      var lastUrl = pref.getComplexValue("general.open_location.last_url",
+                                         Components.interfaces.nsISupportsWString).data;
+      urlbarHistButton.disabled = ( urlBarHist.count == 0 && !lastUrl ) || isBtnLocked ;
     }
     catch(ex) {
-    } 
+    }
+    
+    var globalHistButton = document.getElementById("browserClearHistory");
+    var globalHistory = Components.classes["@mozilla.org/browser/global-history;1"]
+                                  .getService(Components.interfaces.nsIBrowserHistory);
+    if (globalHistory.count == 0)
+      globalHistButton.disabled = true;
+
   }
 
   function onHistoryOK()
@@ -93,6 +104,14 @@
     var urlBarHistory = Components.classes["@mozilla.org/browser/urlbarhistory;1"]
                                   .getService(Components.interfaces.nsIUrlbarHistory);
     urlBarHistory.clearHistory();
+    var pref = Components.classes["@mozilla.org/preferences-service;1"]
+                         .getService(Components.interfaces.nsIPrefBranch);
+    var str = Components.classes["@mozilla.org/supports-wstring;1"]
+                         .createInstance(Components.interfaces.nsISupportsWString);
+    str.data = "";
+    pref.setComplexValue("general.open_location.last_url",
+                         Components.interfaces.nsISupportsWString,
+                         str);
     button.setAttribute("disabled","true");
   }
   ]]>