1 files changed, 48 insertions, 0 deletions
diff --git a/browser/base/content/test/general/browser_bug585785.js b/browser/base/content/test/general/browser_bug585785.js
new file mode 100644
index 0000000000..23e0c5ddf5
--- /dev/null
+++ b/browser/base/content/test/general/browser_bug585785.js
@@ -0,0 +1,48 @@
+var tab;
+
+function test() {
+  waitForExplicitFinish();
+
+  // Force-enable tab animations
+  gReduceMotionOverride = false;
+
+  tab = BrowserTestUtils.addTab(gBrowser);
+  isnot(
+    tab.getAttribute("fadein"),
+    "true",
+    "newly opened tab is yet to fade in"
+  );
+
+  // Try to remove the tab right before the opening animation's first frame
+  window.requestAnimationFrame(checkAnimationState);
+}
+
+function checkAnimationState() {
+  is(tab.getAttribute("fadein"), "true", "tab opening animation initiated");
+
+  info(window.getComputedStyle(tab).maxWidth);
+  gBrowser.removeTab(tab, { animate: true });
+  if (!tab.parentNode) {
+    ok(
+      true,
+      "tab removed synchronously since the opening animation hasn't moved yet"
+    );
+    finish();
+    return;
+  }
+
+  info(
+    "tab didn't close immediately, so the tab opening animation must have started moving"
+  );
+  info("waiting for the tab to close asynchronously");
+  tab.addEventListener(
+    "TabAnimationEnd",
+    function listener() {
+      executeSoon(function () {
+        ok(!tab.parentNode, "tab removed asynchronously");
+        finish();
+      });
+    },
+    { once: true }
+  );
+}