--- a/browser/base/content/tabbrowser.js
+++ b/browser/base/content/tabbrowser.js
@@ -2377,22 +2377,17 @@ window._gBrowser = {
       if (typeof index != "number") {
         // Move the new tab after another tab if needed.
         if (!bulkOrderedOpen &&
             ((openerTab &&
               Services.prefs.getBoolPref("browser.tabs.insertRelatedAfterCurrent")) ||
              Services.prefs.getBoolPref("browser.tabs.insertAfterCurrent"))) {
 
           let lastRelatedTab = openerTab && this._lastRelatedTabMap.get(openerTab);
-          let previousTab = (lastRelatedTab || openerTab || this.selectedTab);
-          if (previousTab.multiselected) {
-            index = this.selectedTabs[this.selectedTabs.length - 1]._tPos + 1;
-          } else {
-            index = previousTab._tPos + 1;
-          }
+          index = (lastRelatedTab || openerTab || this.selectedTab)._tPos + 1;
 
           if (lastRelatedTab) {
             lastRelatedTab.owner = null;
           } else if (openerTab) {
             t.owner = openerTab;
           }
           // Always set related map if opener exists.
           if (openerTab) {

--- a/browser/base/content/test/tabs/browser.ini
+++ b/browser/base/content/test/tabs/browser.ini
@@ -28,17 +28,16 @@ support-files =
 [browser_multiselect_tabs_close.js]
 [browser_multiselect_tabs_copy_through_drag_and_drop.js]
 [browser_multiselect_tabs_drag_to_bookmarks_toolbar.js]
 [browser_multiselect_tabs_duplicate.js]
 [browser_multiselect_tabs_event.js]
 [browser_multiselect_tabs_move_to_another_window_drag.js]
 [browser_multiselect_tabs_move_to_new_window_contextmenu.js]
 [browser_multiselect_tabs_mute_unmute.js]
-[browser_multiselect_tabs_open_related.js]
 [browser_multiselect_tabs_pin_unpin.js]
 [browser_multiselect_tabs_positional_attrs.js]
 [browser_multiselect_tabs_reload.js]
 [browser_multiselect_tabs_reopen_in_container.js]
 [browser_multiselect_tabs_reorder.js]
 [browser_multiselect_tabs_using_Ctrl.js]
 [browser_multiselect_tabs_using_keyboard.js]
 skip-if = os == 'mac' # Skipped because macOS keyboard support requires changing system settings

deleted file mode 100644
--- a/browser/base/content/test/tabs/browser_multiselect_tabs_open_related.js
+++ /dev/null
@@ -1,99 +0,0 @@
-const PREF_MULTISELECT_TABS = "browser.tabs.multiselect";
-
-add_task(async function test() {
-  await SpecialPowers.pushPrefEnv({
-    set: [
-      [PREF_MULTISELECT_TABS, true],
-    ],
-  });
-
-  let tab1 = await addTab("http://example.com/1");
-  let tab2 = await addTab("http://example.com/2");
-  let tab3 = await addTab("http://example.com/3");
-
-  await BrowserTestUtils.switchTab(gBrowser, tab1);
-  await triggerClickOn(tab2, { ctrlKey: true });
-
-  ok(tab1.multiselected, "Tab1 is multi-selected");
-  ok(tab2.multiselected, "Tab2 is multi-selected");
-  ok(!tab3.multiselected, "Tab3 is not multi-selected");
-
-  let tabs = document.getElementById("tabbrowser-tabs");
-  let newTabButton = document.getAnonymousElementByAttribute(tabs, "anonid", "tabs-newtab-button");
-  let promiseTabOpened = BrowserTestUtils.waitForEvent(gBrowser.tabContainer, "TabOpen");
-  EventUtils.synthesizeMouseAtCenter(newTabButton, {ctrlKey: true});
-  let openEvent = await promiseTabOpened;
-  let newTab = openEvent.target;
-
-  is(newTab.previousElementSibling, tab2,
-    "New tab should be opened after tab2 when tab1 and tab2 are multiselected");
-  is(newTab.nextElementSibling, tab3,
-    "New tab should be opened before tab3 when tab1 and tab2 are multiselected");
-  BrowserTestUtils.removeTab(newTab);
-
-  await BrowserTestUtils.switchTab(gBrowser, tab1);
-  ok(!tab1.multiselected, "Tab1 is not multi-selected");
-  ok(!tab2.multiselected, "Tab2 is not multi-selected");
-  ok(!tab3.multiselected, "Tab3 is not multi-selected");
-
-  promiseTabOpened = BrowserTestUtils.waitForEvent(gBrowser.tabContainer, "TabOpen");
-  EventUtils.synthesizeMouseAtCenter(newTabButton, {ctrlKey: true});
-  openEvent = await promiseTabOpened;
-  newTab = openEvent.target;
-  is(newTab.previousElementSibling, tab1,
-    "New tab should be opened after tab1 when only tab1 is selected");
-  is(newTab.nextElementSibling, tab2,
-    "New tab should be opened before tab2 when only tab1 is selected");
-  BrowserTestUtils.removeTab(newTab);
-
-  await BrowserTestUtils.switchTab(gBrowser, tab1);
-  await triggerClickOn(tab3, { ctrlKey: true });
-  ok(tab1.multiselected, "Tab1 is multi-selected");
-  ok(!tab2.multiselected, "Tab2 is not multi-selected");
-  ok(tab3.multiselected, "Tab3 is multi-selected");
-
-  promiseTabOpened = BrowserTestUtils.waitForEvent(gBrowser.tabContainer, "TabOpen");
-  EventUtils.synthesizeMouseAtCenter(newTabButton, {ctrlKey: true});
-  openEvent = await promiseTabOpened;
-  newTab = openEvent.target;
-  is(newTab.previousElementSibling, tab3,
-    "New tab should be opened after tab3 when tab1 and tab3 are selected");
-  is(newTab.nextElementSibling, null,
-    "New tab should be opened at the end of the tabstrip when tab1 and tab3 are selected");
-  BrowserTestUtils.removeTab(newTab);
-
-  await BrowserTestUtils.switchTab(gBrowser, tab1);
-  ok(!tab1.multiselected, "Tab1 is not multi-selected");
-  ok(!tab2.multiselected, "Tab2 is not multi-selected");
-  ok(!tab3.multiselected, "Tab3 is not multi-selected");
-
-  promiseTabOpened = BrowserTestUtils.waitForEvent(gBrowser.tabContainer, "TabOpen");
-  EventUtils.synthesizeMouseAtCenter(newTabButton, {});
-  openEvent = await promiseTabOpened;
-  newTab = openEvent.target;
-  is(newTab.previousElementSibling, tab3,
-    "New tab should be opened after tab3 when ctrlKey is not used without multiselection");
-  is(newTab.nextElementSibling, null,
-    "New tab should be opened at the end of the tabstrip when ctrlKey is not used without multiselection");
-  BrowserTestUtils.removeTab(newTab);
-
-  await BrowserTestUtils.switchTab(gBrowser, tab1);
-  await triggerClickOn(tab2, { ctrlKey: true });
-  ok(tab1.multiselected, "Tab1 is multi-selected");
-  ok(tab2.multiselected, "Tab2 is multi-selected");
-  ok(!tab3.multiselected, "Tab3 is not multi-selected");
-
-  promiseTabOpened = BrowserTestUtils.waitForEvent(gBrowser.tabContainer, "TabOpen");
-  EventUtils.synthesizeMouseAtCenter(newTabButton, {});
-  openEvent = await promiseTabOpened;
-  newTab = openEvent.target;
-  is(newTab.previousElementSibling, tab3,
-    "New tab should be opened after tab3 when ctrlKey is not used with multiselection");
-  is(newTab.nextElementSibling, null,
-    "New tab should be opened at the end of the tabstrip when ctrlKey is not used with multiselection");
-  BrowserTestUtils.removeTab(newTab);
-
-  BrowserTestUtils.removeTab(tab1);
-  BrowserTestUtils.removeTab(tab2);
-  BrowserTestUtils.removeTab(tab3);
-});