--- a/addon-sdk/source/lib/sdk/panel.js
+++ b/addon-sdk/source/lib/sdk/panel.js
@@ -132,16 +132,17 @@ const Panel = Class({
   setup: function setup(options) {
     let model = merge({
       defaultWidth: 320,
       defaultHeight: 240,
       focus: true,
       position: Object.freeze({}),
       contextMenu: false
     }, panelContract(options));
+    model.ready = false;
     models.set(this, model);
 
     if (model.contentStyle || model.contentStyleFile) {
       styles.set(this, Style({
         uri: model.contentStyleFile,
         source: model.contentStyle
       }));
     }
@@ -295,25 +296,40 @@ let hides = filter(panelEvents, ({type})
 let ready = filter(panelEvents, ({type, target}) =>
   getAttachEventType(modelFor(panelFor(target))) === type);
 
 // Styles should be always added as soon as possible, and doesn't makes them
 // depends on `contentScriptWhen`
 let start = filter(panelEvents, ({type}) => type === "document-element-inserted");
 
 // Forward panel show / hide events to panel's own event listeners.
-on(shows, "data", ({target}) => emit(panelFor(target), "show"));
+on(shows, "data", ({target}) => {
+  let panel = panelFor(target);
+  if (modelFor(panel).ready)
+    emit(panel, "show");
+});
 
-on(hides, "data", ({target}) => emit(panelFor(target), "hide"));
+on(hides, "data", ({target}) => {
+  let panel = panelFor(target);
+  if (modelFor(panel).ready)
+    emit(panel, "hide");
+});
 
 on(ready, "data", ({target}) => {
   let panel = panelFor(target);
   let window = domPanel.getContentDocument(target).defaultView;
 
   workerFor(panel).attach(window);
+
+  if (!modelFor(panel).ready) {
+    modelFor(panel).ready = true;
+
+    if (viewFor(panel).state == "open")
+      emit(panel, "show");
+  }
 });
 
 on(start, "data", ({target}) => {
   let panel = panelFor(target);
   let window = domPanel.getContentDocument(target).defaultView;
 
   attach(styleFor(panel), window);
 });

--- a/addon-sdk/source/test/test-panel.js
+++ b/addon-sdk/source/test/test-panel.js
@@ -276,27 +276,38 @@ exports["test Resize Panel"] = function(
     browserWindow.focus();
   }
 };
 
 exports["test Hide Before Show"] = function(assert, done) {
   const { Panel } = require('sdk/panel');
 
   let showCalled = false;
-  let panel = Panel({
+  let hideCalled = false;
+  let panel1 = Panel({
     onShow: function () {
       showCalled = true;
     },
     onHide: function () {
-      assert.ok(!showCalled, 'must not emit show if was hidden before');
-      done();
+      hideCalled = true;
     }
   });
-  panel.show();
-  panel.hide();
+  panel1.show();
+  panel1.hide();
+
+  let panel2 = Panel({
+    onShow: function () {
+      assert.ok(!showCalled, 'should not emit show');
+      assert.ok(!hideCalled, 'should not emit hide');
+      panel1.destroy();
+      panel2.destroy();
+      done();
+    },
+  });
+  panel2.show();
 };
 
 exports["test Several Show Hides"] = function(assert, done) {
   const { Panel } = require('sdk/panel');
 
   let hideCalled = 0;
   let panel = Panel({
     contentURL: "about:buildconfig",
@@ -1274,16 +1285,57 @@ exports["test panel addon global object"
 
   yield wait(panel.port, "document-to-addon");
 
   assert.pass("Received an event from the document");
 
   loader.unload();
 }
 
+exports["test panel load doesn't show"] = function*(assert) {
+  let loader = Loader(module);
+
+  let showCount = 0;
+  let panel = loader.require("sdk/panel").Panel({
+    contentScript: "addEventListener('load', function(event) { self.postMessage('load'); });",
+    contentScriptWhen: "start",
+    contentURL: "data:text/html;charset=utf-8,",
+  });
+
+  let shown = defer();
+  let messaged = defer();
+
+  panel.once("show", function() {
+    shown.resolve();
+  });
+
+  panel.once("message", function() {
+    messaged.resolve();
+  });
+
+  panel.show();
+  yield all([shown.promise, messaged.promise]);
+  assert.ok(true, "Saw panel display");
+
+  panel.on("show", function() {
+    assert.fail("Should not have seen another show event")
+  });
+
+  messaged = defer();
+  panel.once("message", function() {
+    assert.ok(true, "Saw panel reload");
+    messaged.resolve();
+  });
+
+  panel.contentURL = "data:text/html;charset=utf-8,<html/>";
+
+  yield messaged.promise;
+  loader.unload();
+}
+
 if (isWindowPBSupported) {
   exports.testGetWindow = function(assert, done) {
     let activeWindow = getMostRecentBrowserWindow();
     open(null, { features: {
       toolbar: true,
       chrome: true,
       private: true
     } }).then(window => {