Bug 678480 - First-run animation is busted and tab sidebar is visible at startup r=wjohnston

mobile/chrome/content/aboutHome.xhtml

@@ -427,8 +427,10 @@
    
    function startDiscovery() {
      let win = getChromeWin();
+
+     // If a sidebar is completely open, just bail
      let [leftWidth, rightWidth] = win.Browser.computeSidebarVisibility();
-     if (leftWidth > 0 || rightWidth > 0) {
+     if (leftWidth == 1 || rightWidth == 1) {
        endDiscovery();
        return;
      }
@@ -451,7 +453,6 @@
    }
    
    function initLightbox() {
-
      let prefs = getChromeWin().Services.prefs;
      let channel = prefs.getCharPref("app.update.channel");
      let startupCount = 0;

mobile/chrome/content/browser.js

@@ -278,8 +278,16 @@ var Browser = {
       // Restore the previous scroll position
       let restorePosition = Browser.controlsPosition || { hideSidebars: true };
       if (restorePosition.hideSidebars) {
-        restorePosition.hideSidebars = false;
+        // Since this happens early in the startup process, we need to make sure
+        // the UI has really responded
+        let x = {}, y = {};
         Browser.hideSidebars();
+        Browser.controlsScrollboxScroller.getPosition(x, y);
+        if (x.value > 0) {
+          // Update the control position data so we are set correctly for the next resize
+          restorePosition.hideSidebars = false;
+          restorePosition.x = x.value;
+        }
       } else {
         // Handle Width transformation of the tabs sidebar
         if (restorePosition.x) {