diff --git a/browser/components/customizableui/CustomizableWidgets.jsm b/browser/components/customizableui/CustomizableWidgets.jsm
index ad2b69fddbee..76efb06ed6ec 100644
--- a/browser/components/customizableui/CustomizableWidgets.jsm
+++ b/browser/components/customizableui/CustomizableWidgets.jsm
@@ -957,9 +957,8 @@ const CustomizableWidgets = [
     type: "custom",
     label: "loop-call-button3.label",
     tooltiptext: "loop-call-button3.tooltiptext",
+    privateBrowsingTooltiptext: "loop-call-button3-pb.tooltiptext",
     defaultArea: CustomizableUI.AREA_NAVBAR,
-    // Not in private browsing, see bug 1108187.
-    showInPrivateBrowsing: false,
     introducedInVersion: 4,
     onBuild: function(aDocument) {
       // If we're not supposed to see the button, return zip.
@@ -967,13 +966,21 @@ const CustomizableWidgets = [
         return null;
       }
 
+      let isWindowPrivate = PrivateBrowsingUtils.isWindowPrivate(aDocument.defaultView);
+
       let node = aDocument.createElementNS(kNSXUL, "toolbarbutton");
       node.setAttribute("id", this.id);
       node.classList.add("toolbarbutton-1");
       node.classList.add("chromeclass-toolbar-additional");
       node.classList.add("badged-button");
       node.setAttribute("label", CustomizableUI.getLocalizedProperty(this, "label"));
-      node.setAttribute("tooltiptext", CustomizableUI.getLocalizedProperty(this, "tooltiptext"));
+      if (isWindowPrivate)
+        node.setAttribute("disabled", "true");
+      let tooltiptext = isWindowPrivate ?
+        CustomizableUI.getLocalizedProperty(this, "privateBrowsingTooltiptext",
+          [CustomizableUI.getLocalizedProperty(this, "label")]) :
+        CustomizableUI.getLocalizedProperty(this, "tooltiptext");
+      node.setAttribute("tooltiptext", tooltiptext);
       node.setAttribute("removable", "true");
       node.addEventListener("command", function(event) {
         aDocument.defaultView.LoopUI.togglePanel(event);
diff --git a/browser/components/loop/test/mochitest/.eslintrc b/browser/components/loop/test/mochitest/.eslintrc
index 7a196541186a..5833aeeb7f89 100644
--- a/browser/components/loop/test/mochitest/.eslintrc
+++ b/browser/components/loop/test/mochitest/.eslintrc
@@ -21,6 +21,7 @@
     "gMozLoopAPI": true,
     "mockDb": true,
     "mockPushHandler": true,
+    "OpenBrowserWindow": true,
     "promiseDeletedOAuthParams": false,
     "promiseOAuthGetRegistration": false,
     "promiseOAuthParamsSetup": false,
diff --git a/browser/components/loop/test/mochitest/browser_toolbarbutton.js b/browser/components/loop/test/mochitest/browser_toolbarbutton.js
index 95b8ed32560e..1bb2285c12da 100644
--- a/browser/components/loop/test/mochitest/browser_toolbarbutton.js
+++ b/browser/components/loop/test/mochitest/browser_toolbarbutton.js
@@ -167,3 +167,19 @@ add_task(function* test_screen_share() {
   MozLoopService.setScreenShareState("1", false);
   Assert.strictEqual(LoopUI.toolbarButton.node.getAttribute("state"), "", "Check button is in default state");
 });
+
+add_task(function* test_private_browsing_window() {
+  let win = OpenBrowserWindow({ private: true });
+  yield new Promise(resolve => {
+    win.addEventListener("load", function listener() {
+      win.removeEventListener("load", listener);
+      resolve();
+    });
+  });
+
+  let button = win.LoopUI.toolbarButton.node;
+  Assert.ok(button, "Loop button should be present");
+  Assert.ok(button.getAttribute("disabled"), "Disabled attribute should be set");
+
+  win.close();
+});
diff --git a/browser/locales/en-US/chrome/browser/customizableui/customizableWidgets.properties b/browser/locales/en-US/chrome/browser/customizableui/customizableWidgets.properties
index f61b20c17d89..f0ca0b10826b 100644
--- a/browser/locales/en-US/chrome/browser/customizableui/customizableWidgets.properties
+++ b/browser/locales/en-US/chrome/browser/customizableui/customizableWidgets.properties
@@ -97,6 +97,9 @@ quit-button.tooltiptext.mac = Quit %1$S (%2$S)
 # approval before you change it.
 loop-call-button3.label = Hello
 loop-call-button3.tooltiptext = Start a conversation
+# LOCALIZATION NOTE(loop-call-button3-pb.tooltiptext): Shown when the button is
+# placed inside a Private Browsing window. %S is the value of loop-call-button3.label.
+loop-call-button3-pb.tooltiptext = %S is not available in Private Browsing
 
 social-share-button.label = Share This Page
 social-share-button.tooltiptext = Share this page