Bug 1336227 - Show about:blank as soon as possible during startup (pref'ed off), r=mconley.

browser/app/profile/firefox.js

@@ -257,6 +257,9 @@ pref("browser.startup.homepage",            "chrome://branding/locale/browsercon
 // Whether we should skip the homepage when opening the first-run page
 pref("browser.startup.firstrunSkipsHomepage", true);
 
+// Show an about:blank window as early as possible for quick startup feedback.
+pref("browser.startup.blankWindow", false);
+
 pref("browser.slowStartup.notificationDisabled", false);
 pref("browser.slowStartup.timeThreshold", 20000);
 pref("browser.slowStartup.maxSamples", 5);

browser/components/nsBrowserContentHandler.js

@@ -797,10 +797,27 @@ nsDefaultCommandLineHandler.prototype = {
           return;
         }
       }
+      if (cmdLine.state == nsICommandLine.STATE_INITIAL_LAUNCH) {
+        let win = Services.wm.getMostRecentWindow("navigator:blank");
+        if (win) {
+          win.location = gBrowserContentHandler.chromeURL;
+          win.arguments = [gBrowserContentHandler.defaultArgs];
+          return;
+        }
+      }
+
       // Passing defaultArgs, so use NO_EXTERNAL_URIS
       openWindow(null, gBrowserContentHandler.chromeURL, "_blank",
                  "chrome,dialog=no,all" + gBrowserContentHandler.getFeatures(cmdLine),
                  gBrowserContentHandler.defaultArgs, NO_EXTERNAL_URIS);
+    } else {
+      // Need a better solution in the future to avoid opening the blank window
+      // when command line parameters say we are not going to show a browser
+      // window, but for now the blank window getting closed quickly (and
+      // causing only a slight flicker) is better than leaving it open.
+      let win = Services.wm.getMostRecentWindow("navigator:blank");
+      if (win)
+        win.close();
     }
   },
 

browser/components/nsBrowserGlue.js

@@ -8,6 +8,69 @@ ChromeUtils.import("resource://gre/modules/XPCOMUtils.jsm");
 ChromeUtils.import("resource://gre/modules/Services.jsm");
 ChromeUtils.import("resource://gre/modules/AppConstants.jsm");
 
+(function earlyBlankFirstPaint() {
+  if (!Services.prefs.getBoolPref("browser.startup.blankWindow", false))
+    return;
+
+  let store = Cc["@mozilla.org/xul/xulstore;1"].getService(Ci.nsIXULStore);
+  let getValue = attr =>
+    store.getValue("chrome://browser/content/browser.xul", "main-window", attr);
+  let width = getValue("width");
+  let height = getValue("height");
+
+  // The clean profile case isn't handled yet. Return early for now.
+  if (!width || !height)
+    return;
+
+  let screenX = getValue("screenX");
+  let screenY = getValue("screenY");
+  let browserWindowFeatures =
+    "chrome,all,dialog=no,extrachrome,menubar,resizable,scrollbars,status," +
+    "location,toolbar,personalbar," +
+    `left=${screenX},top=${screenY}`;
+
+  if (Services.prefs.getBoolPref("browser.suppress_first_window_animation"))
+    browserWindowFeatures += ",suppressanimation";
+
+  let win = Services.ww.openWindow(null, "about:blank", null,
+                                   browserWindowFeatures, null);
+
+  // Hide the titlebar if the actual browser window will draw in it.
+  if (Services.prefs.getBoolPref("browser.tabs.drawInTitlebar")) {
+    win.QueryInterface(Ci.nsIInterfaceRequestor)
+       .getInterface(Ci.nsIDOMWindowUtils)
+       .setChromeMargin(0, 2, 2, 2);
+  }
+
+  if (AppConstants.platform != "macosx") {
+    // On Windows/Linux the position is in device pixels rather than CSS pixels.
+    let scale = win.devicePixelRatio;
+    if (scale > 1)
+      win.moveTo(screenX / scale, screenY / scale);
+  }
+
+  // The sizemode="maximized" attribute needs to be set before first paint.
+  let docElt = win.document.documentElement;
+  let sizemode = getValue("sizemode");
+  if (sizemode == "maximized") {
+    docElt.setAttribute("sizemode", sizemode);
+
+    // Needed for when the user leaves the maximized mode.
+    docElt.setAttribute("height", height);
+    docElt.setAttribute("width", width);
+  } else {
+    // Setting the size of the window in the features string instead of here
+    // causes the window to grow by the size of the titlebar.
+    win.resizeTo(width, height);
+  }
+
+  // The window becomes visible after OnStopRequest, so make this happen now.
+  win.stop();
+
+  // Used in nsBrowserContentHandler.js to close unwanted blank windows.
+  docElt.setAttribute("windowtype", "navigator:blank");
+})();
+
 Cu.importGlobalProperties(["fetch"]);
 
 XPCOMUtils.defineLazyServiceGetter(this, "WindowsUIUtils", "@mozilla.org/windows-ui-utils;1", "nsIWindowsUIUtils");