--- a/browser/metro/base/content/Util.js
+++ b/browser/metro/base/content/Util.js
@@ -78,40 +78,54 @@ let Util = {
   },
 
   isTextInput: function isTextInput(aElement) {
     return ((aElement instanceof Ci.nsIDOMHTMLInputElement &&
              aElement.mozIsTextField(false)) ||
             aElement instanceof Ci.nsIDOMHTMLTextAreaElement);
   },
 
+  /**
+   * Checks whether aElement's content can be edited either if it(or any of its
+   * parents) has "contenteditable" attribute set to "true" or aElement's
+   * ownerDocument is in design mode.
+   */
   isEditableContent: function isEditableContent(aElement) {
-    if (!aElement)
-      return false;
-    if (aElement.isContentEditable || aElement.designMode == "on")
-      return true;
-    return false;
+    return !!aElement && (aElement.isContentEditable ||
+                          this.isOwnerDocumentInDesignMode(aElement));
+
   },
 
   isEditable: function isEditable(aElement) {
-    if (!aElement)
+    if (!aElement) {
       return false;
-    if (this.isTextInput(aElement) || this.isEditableContent(aElement))
+    }
+
+    if (this.isTextInput(aElement) || this.isEditableContent(aElement)) {
       return true;
+    }
 
     // If a body element is editable and the body is the child of an
     // iframe or div we can assume this is an advanced HTML editor
     if ((aElement instanceof Ci.nsIDOMHTMLIFrameElement ||
          aElement instanceof Ci.nsIDOMHTMLDivElement) &&
         aElement.contentDocument &&
         this.isEditableContent(aElement.contentDocument.body)) {
       return true;
     }
 
-    return aElement.ownerDocument && aElement.ownerDocument.designMode == "on";
+    return false;
+  },
+
+  /**
+   * Checks whether aElement's owner document has design mode turned on.
+   */
+  isOwnerDocumentInDesignMode: function(aElement) {
+    return !!aElement && !!aElement.ownerDocument &&
+           aElement.ownerDocument.designMode == "on";
   },
 
   isMultilineInput: function isMultilineInput(aElement) {
     return (aElement instanceof Ci.nsIDOMHTMLTextAreaElement);
   },
 
   isLink: function isLink(aElement) {
     return ((aElement instanceof Ci.nsIDOMHTMLAnchorElement && aElement.href) ||

--- a/browser/metro/base/content/contenthandlers/ContextMenuHandler.js
+++ b/browser/metro/base/content/contenthandlers/ContextMenuHandler.js
@@ -100,33 +100,35 @@ var ContextMenuHandler = {
   /******************************************************
    * ContextCommand handlers
    */
 
   _onSelectAll: function _onSelectAll() {
     if (Util.isTextInput(this._target)) {
       // select all text in the input control
       this._target.select();
+    } else if (Util.isEditableContent(this._target)) {
+      this._target.ownerDocument.execCommand("selectAll", false);
     } else {
       // select the entire document
       content.getSelection().selectAllChildren(content.document);
     }
     this.reset();
   },
 
   _onPaste: function _onPaste() {
     // paste text if this is an input control
     if (Util.isTextInput(this._target)) {
       let edit = this._target.QueryInterface(Ci.nsIDOMNSEditableElement);
       if (edit) {
         edit.editor.paste(Ci.nsIClipboard.kGlobalClipboard);
       } else {
         Util.dumpLn("error: target element does not support nsIDOMNSEditableElement");
       }
-    } else if (this._target.isContentEditable) {
+    } else if (Util.isEditableContent(this._target)) {
       try {
         this._target.ownerDocument.execCommand("paste",
                                                false,
                                                Ci.nsIClipboard.kGlobalClipboard);
       } catch (ex) {
         dump("ContextMenuHandler: exception pasting into contentEditable: " + ex.message + "\n");
       }
     }
@@ -140,17 +142,17 @@ var ContextMenuHandler = {
   _onCut: function _onCut() {
     if (Util.isTextInput(this._target)) {
       let edit = this._target.QueryInterface(Ci.nsIDOMNSEditableElement);
       if (edit) {
         edit.editor.cut();
       } else {
         Util.dumpLn("error: target element does not support nsIDOMNSEditableElement");
       }
-    } else if (this._target.isContentEditable) {
+    } else if (Util.isEditableContent(this._target)) {
       try {
         this._target.ownerDocument.execCommand("cut", false);
       } catch (ex) {
         dump("ContextMenuHandler: exception cutting from contentEditable: " + ex.message + "\n");
       }
     }
     this.reset();
   },
@@ -254,17 +256,19 @@ var ContextMenuHandler = {
           linkUrl = state.linkURL;
           state.linkTitle = popupNode.textContent || popupNode.title;
           state.linkProtocol = this._getProtocol(this._getURI(state.linkURL));
           // mark as text so we can pickup on selection below
           isText = true;
           break;
         }
         // is the target contentEditable (not just inheriting contentEditable)
-        else if (elem.contentEditable == "true") {
+        // or the entire document in designer mode.
+        else if (elem.contentEditable == "true" ||
+                 Util.isOwnerDocumentInDesignMode(elem)) {
           this._target = elem;
           isEditableText = true;
           isText = true;
           uniqueStateTypes.add("input-text");
 
           if (elem.textContent.length) {
             uniqueStateTypes.add("selectable");
           } else {

--- a/browser/metro/base/tests/mochitest/browser_context_menu_tests.js
+++ b/browser/metro/base/tests/mochitest/browser_context_menu_tests.js
@@ -704,12 +704,90 @@ gTests.push({
 
 gTests.push({
   desc: "bug 856264 - touch - context menu should reopen on other links",
   setUp: reopenSetUp,
   tearDown: reopenTearDown,
   run: getReopenTest(sendContextMenuClickToElement, sendTap)
 });
 
+gTests.push({
+  desc: "Bug 947505 - Right-click in a designMode document should display a " +
+        "context menu",
+  run: function test() {
+    info(chromeRoot + "browser_context_menu_tests_02.html");
+    yield addTab(chromeRoot + "browser_context_menu_tests_02.html");
+
+    purgeEventQueue();
+    emptyClipboard();
+    ContextUI.dismiss();
+
+    yield waitForCondition(() => !ContextUI.navbarVisible);
+
+    let tabWindow = Browser.selectedTab.browser.contentWindow;
+    let testSpan = tabWindow.document.getElementById("text1");
+
+    // Case #1: Document isn't in design mode and nothing is selected.
+    tabWindow.document.designMode = "off";
+
+    // Simulate right mouse click to reproduce the same step as noted in the
+    // appropriate bug. It's valid for non-touch case only.
+    synthesizeNativeMouseRDown(Browser.selectedTab.browser, 10, 10);
+    synthesizeNativeMouseRUp(Browser.selectedTab.browser, 10, 10);
+
+    yield waitForCondition(() => ContextUI.navbarVisible);
+
+    ok(ContextUI.navbarVisible, "Navbar is visible on context menu action.");
+    ok(ContextUI.tabbarVisible, "Tabbar is visible on context menu action.");
+
+    ContextUI.dismiss();
+    yield waitForCondition(() => !ContextUI.navbarVisible);
+
+    // Case #2: Document isn't in design mode and text is selected.
+    tabWindow.getSelection().selectAllChildren(testSpan);
+
+    let promise = waitForEvent(tabWindow.document, "popupshown");
+    sendContextMenuClickToSelection(tabWindow);
+    yield promise;
+
+    checkContextUIMenuItemVisibility(["context-copy", "context-search"]);
+
+    promise = waitForEvent(document, "popuphidden");
+    ContextMenuUI.hide();
+    yield promise;
+
+    // Case #3: Document is in design mode and nothing is selected.
+    tabWindow.document.designMode = "on";
+    tabWindow.getSelection().removeAllRanges();
+
+    promise = waitForEvent(tabWindow.document, "popupshown");
+    sendContextMenuClickToElement(tabWindow, testSpan);
+    yield promise;
+
+    checkContextUIMenuItemVisibility(["context-select-all", "context-select"]);
+
+    promise = waitForEvent(document, "popuphidden");
+    ContextMenuUI.hide();
+    yield promise;
+
+    // Case #4: Document is in design mode and text is selected.
+    tabWindow.getSelection().selectAllChildren(testSpan);
+
+    promise = waitForEvent(tabWindow.document, "popupshown");
+    sendContextMenuClickToSelection(tabWindow);
+    yield promise;
+
+    checkContextUIMenuItemVisibility(["context-cut", "context-copy",
+                                      "context-select-all", "context-select",
+                                      "context-search"]);
+
+    promise = waitForEvent(document, "popuphidden");
+    ContextMenuUI.hide();
+    yield promise;
+
+    Browser.closeTab(Browser.selectedTab, { forceClose: true });
+  }
+});
+
 function test() {
   setDevPixelEqualToPx();
   runTests();
 }