diff --git a/browser/components/extensions/ext-windows.js b/browser/components/extensions/ext-windows.js
index 8fdc90423092..ffc054a95c15 100644
--- a/browser/components/extensions/ext-windows.js
+++ b/browser/components/extensions/ext-windows.js
@@ -160,20 +160,16 @@ extensions.registerSchemaAPI("windows", "addon_parent", context => {
         return new Promise(resolve => {
           window.addEventListener("load", function listener() {
             window.removeEventListener("load", listener);
-
-            if (createData.state == "maximized" || createData.state == "normal" ||
-                (createData.state == "fullscreen" && AppConstants.platform != "macosx")) {
+            if (["maximized", "normal"].includes(createData.state)) {
               window.document.documentElement.setAttribute("sizemode", createData.state);
-            } else if (createData.state !== null) {
-              // window.minimize() has no effect until the window has been shown.
-              return promiseObserved("document-shown", doc => doc == window.document).then(() => {
-                WindowManager.setState(window, createData.state);
-                resolve();
-              });
             }
-            resolve();
+            resolve(promiseObserved("browser-delayed-startup-finished", win => win == window));
           });
         }).then(() => {
+          // Some states only work after delayed-startup-finished
+          if (["minimized", "fullscreen", "docked"].includes(createData.state)) {
+            WindowManager.setState(window, createData.state);
+          }
           if (allowScriptsToClose) {
             for (let {linkedBrowser} of window.gBrowser.tabs) {
               onXULFrameLoaderCreated({target: linkedBrowser});
@@ -181,7 +177,7 @@ extensions.registerSchemaAPI("windows", "addon_parent", context => {
                                              "XULFrameLoaderCreated", onXULFrameLoaderCreated);
             }
           }
-          return WindowManager.convert(extension, window);
+          return WindowManager.convert(extension, window, {populate: true});
         });
       },
 
diff --git a/browser/components/extensions/test/browser/browser_ext_windows_create.js b/browser/components/extensions/test/browser/browser_ext_windows_create.js
index 6cb1a26c104b..97a4acf5dc3c 100644
--- a/browser/components/extensions/test/browser/browser_ext_windows_create.js
+++ b/browser/components/extensions/test/browser/browser_ext_windows_create.js
@@ -35,6 +35,7 @@ add_task(function* testWindowCreate() {
             }
           }
 
+          browser.test.assertEq(1, window.tabs.length, "tabs property got populated");
           return checkWindow(expected).then(() => {
             if (keep) {
               return window;
diff --git a/browser/components/extensions/test/browser/browser_ext_windows_create_tabId.js b/browser/components/extensions/test/browser/browser_ext_windows_create_tabId.js
index 3bd586a17f02..2b875f7066a4 100644
--- a/browser/components/extensions/test/browser/browser_ext_windows_create_tabId.js
+++ b/browser/components/extensions/test/browser/browser_ext_windows_create_tabId.js
@@ -24,13 +24,14 @@ add_task(function* testWindowCreate() {
       });
     };
 
-    let windowId;
+    let windowId, tabId;
     browser.windows.getCurrent().then(window => {
       windowId = window.id;
 
       browser.test.log("Create additional tab in window 1");
       return browser.tabs.create({windowId, url: "about:blank"});
     }).then(tab => {
+      tabId = tab.id;
       browser.test.log("Create a new window, adopting the new tab");
 
       // Note that we want to check against actual boolean values for
@@ -39,10 +40,11 @@ add_task(function* testWindowCreate() {
 
       return Promise.all([
         promiseTabAttached(),
-        browser.windows.create({tabId: tab.id}),
+        browser.windows.create({tabId: tabId}),
       ]);
     }).then(([, window]) => {
       browser.test.assertEq(false, window.incognito, "New window is not private");
+      browser.test.assertEq(tabId, window.tabs[0].id, "tabs property populated correctly");
 
       browser.test.log("Close the new window");
       return browser.windows.remove(window.id);
@@ -113,6 +115,10 @@ add_task(function* testWindowCreate() {
 
       return browser.windows.create({url: ["http://example.com/", "http://example.org/"]});
     }).then(window => {
+      browser.test.assertEq(2, window.tabs.length, "2 tabs were opened in new window");
+      browser.test.assertEq("about:blank", window.tabs[0].url, "about:blank, page not loaded yet");
+      browser.test.assertEq("about:blank", window.tabs[1].url, "about:blank, page not loaded yet");
+
       return Promise.all([
         promiseTabUpdated("http://example.com/"),
         promiseTabUpdated("http://example.org/"),
@@ -145,4 +151,3 @@ add_task(function* testWindowCreate() {
   yield extension.awaitFinish("window-create");
   yield extension.unload();
 });
-