diff --git a/browser/components/preferences/in-content/subdialogs.js b/browser/components/preferences/in-content/subdialogs.js
--- a/browser/components/preferences/in-content/subdialogs.js
+++ b/browser/components/preferences/in-content/subdialogs.js
@@ -494,37 +494,11 @@
       return;
     }
 
     let fm = Services.focus;
 
-    let isLastFocusableElement = el => {
-      // XXXgijs unfortunately there is no way to get the last focusable element without asking
-      // the focus manager to move focus to it.
-      let rv =
-        el ==
-        fm.moveFocus(this._frame.contentWindow, null, fm.MOVEFOCUS_LAST, 0);
-      fm.setFocus(el, 0);
-      return rv;
-    };
-
-    let forward = !aEvent.shiftKey;
-    // check if focus is leaving the frame (incl. the close button):
-    if (
-      (aEvent.target == this._closeButton && !forward) ||
-      (isLastFocusableElement(aEvent.originalTarget) && forward)
-    ) {
-      aEvent.preventDefault();
-      aEvent.stopImmediatePropagation();
-      let parentWin = this._getBrowser().ownerGlobal;
-      if (forward) {
-        fm.moveFocus(parentWin, null, fm.MOVEFOCUS_FIRST, fm.FLAG_BYKEY);
-      } else {
-        // Somehow, moving back 'past' the opening doc is not trivial. Cheat by doing it in 2 steps:
-        fm.moveFocus(window, null, fm.MOVEFOCUS_ROOT, fm.FLAG_BYKEY);
-        fm.moveFocus(parentWin, null, fm.MOVEFOCUS_BACKWARD, fm.FLAG_BYKEY);
-      }
-    }
+    // Let's display some error again
   },
 
   _onParentWinFocus(aEvent) {
     // Explicitly check for the focus target of |window| to avoid triggering this when the window
     // is refocused