diff --git a/browser/components/sidebar/browser-sidebar.js b/browser/components/sidebar/browser-sidebar.js
index ef7b67413392840720c8f09b6f22b0413ccf4435..ebbc15722ffb410050dd1923e8bb49d8cd5b6a9e 100644
--- a/browser/components/sidebar/browser-sidebar.js
+++ b/browser/components/sidebar/browser-sidebar.js
@@ -850,7 +850,7 @@ var SidebarController = {
   setPosition() {
     // First reset all ordinals to match DOM ordering.
     let contentArea = document.getElementById("tabbrowser-tabbox");
-    let browser = document.getElementById("browser");
+    let browser = document.getElementById("tabbrowser-tabbox");
     [...browser.children].forEach((node, i, children) => {
       node.style.order = this._positionStart ? i + 1 : children.length - i;
     });
