--- a/browser/base/content/browser.js
+++ b/browser/base/content/browser.js
@@ -6417,16 +6417,21 @@ function checkEmptyPageOrigin(browser = 
   }
   let contentPrincipal = browser.contentPrincipal;
   // Not all principals have URIs...
   if (contentPrincipal.URI) {
     // A manually entered about:blank URI is slightly magical:
     if (uri.spec == "about:blank" && contentPrincipal.isNullPrincipal) {
       return true;
     }
+    // Initial browser loads of URIs when we've changed remoteness means
+    // contentPrincipal hasn't updated.
+    if (contentPrincipal.URI.spec == "about:blank") {
+      return true;
+    }
     return contentPrincipal.URI.equals(uri);
   }
   // ... so for those that don't have them, enforce that the page has the
   // system principal (this matches e.g. on about:newtab).
   let ssm = Services.scriptSecurityManager;
   return ssm.isSystemPrincipal(contentPrincipal);
 }
 

--- a/browser/base/content/test/urlbar/browser_urlbarAboutHomeLoading.js
+++ b/browser/base/content/test/urlbar/browser_urlbarAboutHomeLoading.js
@@ -1,10 +1,12 @@
 "use strict";
 
+const {TabStateFlusher} = Cu.import("resource:///modules/sessionstore/TabStateFlusher.jsm", {});
+
 /**
  * Test what happens if loading a URL that should clear the
  * location bar after a parent process URL.
  */
 add_task(function* clearURLBarAfterParentProcessURL() {
   let tab = yield new Promise(resolve => {
     gBrowser.selectedTab = gBrowser.addTab("about:preferences");
     let newTabBrowser = gBrowser.getBrowserForTab(gBrowser.selectedTab);
@@ -59,8 +61,43 @@ add_task(function* clearURLBarAfterManua
   let aboutHomeLoaded = BrowserTestUtils.browserLoaded(gBrowser.selectedBrowser, false, "about:home");
   EventUtils.sendKey("return");
   yield aboutHomeLoaded;
 
   is(gURLBar.value, "", "URL bar should be empty");
   is(tab.linkedBrowser.userTypedValue, null, "userTypedValue should be null");
   yield BrowserTestUtils.removeTab(tab);
 });
+
+/**
+ * Ensure we don't show 'about:home' in the URL bar temporarily in new tabs
+ * while we're switching remoteness (when the URL we're loading and the
+ * default content principal are different).
+ */
+add_task(function* dontTemporarilyShowAboutHome() {
+  yield SpecialPowers.pushPrefEnv({set: [["browser.startup.page", 1]]});
+  let windowOpenedPromise = BrowserTestUtils.waitForNewWindow();
+  let win = OpenBrowserWindow();
+  yield windowOpenedPromise;
+  win.BrowserOpenTab();
+  yield BrowserTestUtils.switchTab(win.gBrowser, win.gBrowser.selectedTab.nextSibling);
+  yield TabStateFlusher.flush(win.gBrowser.selectedBrowser);
+  yield BrowserTestUtils.closeWindow(win);
+  ok(SessionStore.getClosedWindowCount(), "Should have a closed window");
+
+  windowOpenedPromise = BrowserTestUtils.waitForNewWindow();
+  win = SessionStore.undoCloseWindow(0);
+  yield windowOpenedPromise;
+  let wpl = {
+    onLocationChange(wpl, request, location, flags) {
+      is(win.gURLBar.value, "", "URL bar value should stay empty.");
+    },
+  };
+  win.gBrowser.addProgressListener(wpl);
+  let otherTab = win.gBrowser.selectedTab.previousSibling;
+  let tabLoaded = BrowserTestUtils.browserLoaded(otherTab.linkedBrowser, false, "about:home");
+  yield BrowserTestUtils.switchTab(win.gBrowser, otherTab);
+  yield tabLoaded;
+  win.gBrowser.removeProgressListener(wpl);
+  is(win.gURLBar.value, "", "URL bar value should be empty.");
+
+  yield BrowserTestUtils.closeWindow(win);
+});