--- a/browser/base/content/browser.js
+++ b/browser/base/content/browser.js
@@ -1178,17 +1178,34 @@ var gBrowserInit = {
     Services.telemetry.getHistogramById("E10S_WINDOW").add(gMultiProcessBrowser);
 
     SidebarUI.startDelayedLoad();
 
     UpdateUrlbarSearchSplitterState();
 
     if (!(isBlankPageURL(uriToLoad) || uriToLoad == "about:privatebrowsing") ||
         !focusAndSelectUrlBar()) {
-      gBrowser.selectedBrowser.focus();
+      if (gBrowser.selectedBrowser.isRemoteBrowser) {
+        // If the initial browser is remote, in order to optimize for first paint,
+        // we'll defer switching focus to that browser until it has painted.
+        let focusedElement = document.commandDispatcher.focusedElement;
+        let mm = window.messageManager;
+        mm.addMessageListener("Browser:FirstPaint", function onFirstPaint() {
+          mm.removeMessageListener("Browser:FirstPaint", onFirstPaint);
+          // If focus didn't move while we were waiting for first paint, we're okay
+          // to move to the browser.
+          if (document.commandDispatcher.focusedElement == focusedElement) {
+            gBrowser.selectedBrowser.focus();
+          }
+        });
+      } else {
+        // If the initial browser is not remote, we can focus the browser
+        // immediately with no paint performance impact.
+        gBrowser.selectedBrowser.focus();
+      }
     }
 
     // Enable/Disable auto-hide tabbar
     gBrowser.tabContainer.updateVisibility();
 
     BookmarkingUI.init();
 
     gPrefService.addObserver(gHomeButton.prefDomain, gHomeButton, false);

--- a/browser/base/content/tab-content.js
+++ b/browser/base/content/tab-content.js
@@ -848,8 +848,13 @@ var RefreshBlocker = {
 
 RefreshBlocker.init();
 
 ExtensionContent.init(this);
 addEventListener("unload", () => {
   ExtensionContent.uninit(this);
   RefreshBlocker.uninit();
 });
+
+addEventListener("MozAfterPaint", function onFirstPaint() {
+  removeEventListener("MozAfterPaint", onFirstPaint);
+  sendAsyncMessage("Browser:FirstPaint");
+});