1 files changed, 48 insertions, 0 deletions
diff --git a/toolkit/actors/AutoScrollParent.sys.mjs b/toolkit/actors/AutoScrollParent.sys.mjs
new file mode 100644
index 0000000000..1f9f780902
--- /dev/null
+++ b/toolkit/actors/AutoScrollParent.sys.mjs
@@ -0,0 +1,48 @@
+/* vim: set ts=2 sw=2 sts=2 et tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+export class AutoScrollParent extends JSWindowActorParent {
+  receiveMessage(msg) {
+    let browser = this.manager.browsingContext.top.embedderElement;
+    if (!browser) {
+      return null;
+    }
+
+    // If another tab is activated, we shouldn't start autoscroll requested
+    // for the previous active window if and only if the browser is a remote
+    // browser.  This is required for web apps which don't prevent default of
+    // middle click after opening a new window.  If the active tab is our
+    // documents like about:*, we don't need this check since our documents
+    // should do it correctly.
+    const requestedInForegroundTab = browser.isRemoteBrowser
+      ? Services.focus.focusedElement == browser
+      : true;
+
+    let data = msg.data;
+    switch (msg.name) {
+      case "Autoscroll:Start":
+        // Don't start autoscroll if the tab has already been a background tab.
+        if (!requestedInForegroundTab) {
+          return Promise.resolve({ autoscrollEnabled: false, usingAPZ: false });
+        }
+        return Promise.resolve(browser.startScroll(data));
+      case "Autoscroll:MaybeStartInParent":
+        // Don't start autoscroll if the tab has already been a background tab.
+        if (!requestedInForegroundTab) {
+          return Promise.resolve({ autoscrollEnabled: false, usingAPZ: false });
+        }
+        let parent = this.browsingContext.parent;
+        if (parent) {
+          let actor = parent.currentWindowGlobal.getActor("AutoScroll");
+          actor.sendAsyncMessage("Autoscroll:MaybeStart", data);
+        }
+        break;
+      case "Autoscroll:Cancel":
+        browser.cancelScroll();
+        break;
+    }
+    return null;
+  }
+}