--- a/browser/app/profile/firefox.js
+++ b/browser/app/profile/firefox.js
@@ -431,17 +431,21 @@ pref("browser.link.open_newwindow.restri
 // different.
 #ifdef XP_MACOSX
 pref("browser.link.open_newwindow.disabled_in_fullscreen", true);
 #else
 pref("browser.link.open_newwindow.disabled_in_fullscreen", false);
 #endif
 
 // Tabbed browser
+#if defined(NIGHTLY_BUILD)
+pref("browser.tabs.multiselect", true);
+#else
 pref("browser.tabs.multiselect", false);
+#endif
 pref("browser.tabs.20FpsThrobber", false);
 pref("browser.tabs.30FpsThrobber", false);
 pref("browser.tabs.closeTabByDblclick", false);
 pref("browser.tabs.closeWindowWithLastTab", true);
 // Open related links to a tab, e.g., link in current tab, at next to the
 // current tab if |insertRelatedAfterCurrent| is true.  Otherwise, always
 // append new tab to the end.
 pref("browser.tabs.insertRelatedAfterCurrent", true);

--- a/browser/base/content/test/tabs/browser_multiselect_tabs_using_Ctrl.js
+++ b/browser/base/content/test/tabs/browser_multiselect_tabs_using_Ctrl.js
@@ -1,11 +1,15 @@
 const PREF_MULTISELECT_TABS = "browser.tabs.multiselect";
 
 add_task(async function clickWithoutPrefSet() {
+  await SpecialPowers.pushPrefEnv({
+    set: [[PREF_MULTISELECT_TABS, false]]
+  });
+
   let tab = await addTab();
   let mSelectedTabs = gBrowser._multiSelectedTabsSet;
 
   isnot(gBrowser.selectedTab, tab, "Tab doesn't have focus");
 
   // We make sure that the tab-switch is completely done before executing checks
   await BrowserTestUtils.switchTab(gBrowser, () => {
     triggerClickOn(tab, { ctrlKey: true });
@@ -17,21 +21,25 @@ add_task(async function clickWithoutPref
   ok(!tab.multiselected && !mSelectedTabs.has(tab),
     "Multi-select tab doesn't work when multi-select pref is not set");
   is(gBrowser.selectedTab, tab,
     "Tab has focus, selected tab has changed after Ctrl/Cmd + click");
 
   BrowserTestUtils.removeTab(tab);
 });
 
+add_task(async function setPref() {
+  await SpecialPowers.pushPrefEnv({
+      set: [[PREF_MULTISELECT_TABS, true]]
+  });
+});
+
 add_task(async function clickWithPrefSet() {
   await SpecialPowers.pushPrefEnv({
-    set: [
-      [PREF_MULTISELECT_TABS, true]
-    ]
+    set: [[PREF_MULTISELECT_TABS, true]]
   });
 
   let mSelectedTabs = gBrowser._multiSelectedTabsSet;
   const initialFocusedTab = await addTab();
   await BrowserTestUtils.switchTab(gBrowser, initialFocusedTab);
   const tab = await addTab();
 
   await triggerClickOn(tab, { ctrlKey: true });
@@ -43,22 +51,16 @@ add_task(async function clickWithPrefSet
   ok(!tab.multiselected && !mSelectedTabs.has(tab), "Tab is not (multi) selected anymore");
   is(gBrowser.selectedTab, initialFocusedTab, "Focused tab still doesn't change");
 
   BrowserTestUtils.removeTab(initialFocusedTab);
   BrowserTestUtils.removeTab(tab);
 });
 
 add_task(async function clearSelection() {
-  await SpecialPowers.pushPrefEnv({
-    set: [
-      [PREF_MULTISELECT_TABS, true]
-    ]
-  });
-
   const tab1 = await addTab();
   const tab2 = await addTab();
   const tab3 = await addTab();
 
   await BrowserTestUtils.switchTab(gBrowser, tab1);
   info("We multi-select tab2 with ctrl key down");
   await triggerClickOn(tab2, { ctrlKey: true });
 

--- a/browser/base/content/test/tabs/browser_multiselect_tabs_using_Shift.js
+++ b/browser/base/content/test/tabs/browser_multiselect_tabs_using_Shift.js
@@ -1,11 +1,15 @@
 const PREF_MULTISELECT_TABS = "browser.tabs.multiselect";
 
 add_task(async function prefNotSet() {
+    await SpecialPowers.pushPrefEnv({
+        set: [[PREF_MULTISELECT_TABS, false]]
+    });
+
     let tab1 = await addTab();
     let tab2 = await addTab();
     let tab3 = await addTab();
 
     let mSelectedTabs = gBrowser._multiSelectedTabsSet;
 
     await BrowserTestUtils.switchTab(gBrowser, tab1);
 
@@ -25,19 +29,17 @@ add_task(async function prefNotSet() {
 
     BrowserTestUtils.removeTab(tab1);
     BrowserTestUtils.removeTab(tab2);
     BrowserTestUtils.removeTab(tab3);
 });
 
 add_task(async function setPref() {
     await SpecialPowers.pushPrefEnv({
-        set: [
-            [PREF_MULTISELECT_TABS, true]
-        ]
+        set: [[PREF_MULTISELECT_TABS, true]]
     });
 });
 
 add_task(async function noItemsInTheCollectionBeforeShiftClicking() {
     let tab1 = await addTab();
     let tab2 = await addTab();
     let tab3 = await addTab();
     let tab4 = await addTab();