--- a/browser/base/content/tabbrowser.js
+++ b/browser/base/content/tabbrowser.js
@@ -3417,17 +3417,17 @@ window._gBrowser = {
    * to a new browser window, unless it is (they are) already the only tab(s)
    * in the current window, in which case this will do nothing.
    */
   replaceTabsWithWindow(contextTab) {
     let tabs;
     if (contextTab.multiselected) {
       tabs = this.selectedTabs;
     } else {
-      tabs = [gBrowser.selectedTab];
+      tabs = [contextTab];
     }
 
     if (this.tabs.length == tabs.length) {
       return null;
     }
 
     if (tabs.length == 1) {
       return this.replaceTabWithWindow(tabs[0]);