Keep tabs scroll-locked even if the cursor is moved while the last ta…

…b is being removed #3318

webextensions/background/tree.js

@@ -14,7 +14,7 @@
  * The Original Code is the Tree Style Tab.
  *
  * The Initial Developer of the Original Code is YUKI "Piro" Hiroshi.
- * Portions created by the Initial Developer are Copyright (C) 2011-2021
+ * Portions created by the Initial Developer are Copyright (C) 2011-2023
  * the Initial Developer. All Rights Reserved.
  *
  * Contributor(s): YUKI "Piro" Hiroshi <[email protected]>

webextensions/sidebar/scroll.js

@@ -760,11 +760,23 @@ function tryUnlockPosition(event) {
         log(' => ignore events while the context menu is opened');
         return;
       }
-      if (event.type == 'mousemove' &&
-          (EventUtils.getTabFromEvent(event, { force: true }) ||
-           EventUtils.getTabFromTabbarEvent(event, { force: true }))) {
-        log(' => ignore mousemove on any tab');
-        return;
+      if (event.type == 'mousemove') {
+        if (EventUtils.getTabFromEvent(event, { force: true }) ||
+            EventUtils.getTabFromTabbarEvent(event, { force: true })) {
+          log(' => ignore mousemove on any tab');
+          return;
+        }
+        // When you move mouse while the last tab is being removed, it can fire
+        // a mousemove event on the background area of the tab bar, and it
+        // produces sudden scrolling. So we need to keep scroll locked
+        // while the cursor is still on tabs area.
+        const spacer = mTabBar.querySelector(`.${Constants.kTABBAR_SPACER}`);
+        const pinnedTabsAreaSize = parseFloat(document.documentElement.style.getPropertyValue('--pinned-tabs-area-size'));
+        if ((!spacer || event.clientY < spacer.getBoundingClientRect().top) &&
+            (pinnedTabsAreaSize && !isNaN(pinnedTabsAreaSize) && event.clientY > pinnedTabsAreaSize)) {
+          log(' => ignore mousemove on any tab (removing)');
+          return;
+        }
       }
 
     default: