Remove middle-click new tab preference and associated event handling for vertical tabs

src/browser/app/profile/zen-browser.js

@@ -158,7 +158,6 @@ pref('zen.view.hide-window-controls', true);
 pref('zen.view.experimental-no-window-controls', false);
 
 pref('zen.tabs.dim-pending', true);
-pref('zen.tabs.newtab-on-middle-click', true);
 
 pref('zen.keyboard.shortcuts.enabled', true);
 pref('zen.keyboard.shortcuts.version', 0); // Empty string means default shortcuts
@@ -184,7 +183,6 @@ pref('zen.sidebar.close-on-blur', true);
 pref('zen.sidebar.max-webpanels', 8);
 
 // Zen Split View
-pref('zen.splitView.working', false);
 pref('zen.splitView.min-resize-width', 7);
 pref('zen.splitView.change-on-hover', false);
 pref('zen.splitView.rearrange-hover-size', 24);

src/browser/base/content/ZenUIManager.mjs

@@ -221,23 +221,9 @@ var gZenVerticalTabsManager = {
 
     const tabs = document.getElementById('tabbrowser-tabs');
 
-    XPCOMUtils.defineLazyPreferenceGetter(this, 'canOpenTabOnMiddleClick', 'zen.tabs.newtab-on-middle-click', true);
-
     if (!this.isWindowsStyledButtons) {
       document.documentElement.setAttribute('zen-window-buttons-reversed', true);
     }
-
-    if (tabs) {
-      tabs.addEventListener('mouseup', this.openNewTabOnTabsMiddleClick.bind(this));
-    }
-  },
-
-  openNewTabOnTabsMiddleClick(event) {
-    if (event.button === 1 && event.target.id === 'tabbrowser-tabs' && this.canOpenTabOnMiddleClick) {
-      document.getElementById('cmd_newNavigatorTabNoEvent').doCommand();
-      event.stopPropagation();
-      event.preventDefault();
-    }
   },
 
   toggleExpand() {