--- a/browser/base/content/browser-sidebar.js
+++ b/browser/base/content/browser-sidebar.js
@@ -324,17 +324,17 @@ var SidebarUI = {
 
       let title = sidebarBroadcaster.getAttribute("sidebartitle") ||
                   sidebarBroadcaster.getAttribute("label");
 
       // When loading a web page in the sidebar there is no title set on the
       // broadcaster, as it is instead set by openWebPanel. Don't clear out
       // the title in this case.
       if (title) {
-        this._title.value = title;
+        this.title = title;
       }
 
       let url = sidebarBroadcaster.getAttribute("sidebarurl");
       this.browser.setAttribute("src", url); // kick off async load
 
       if (this.browser.contentDocument.location.href != url) {
         this.browser.addEventListener("load", event => {
 
@@ -383,17 +383,17 @@ var SidebarUI = {
     // create a new content viewer because the old one doesn't get destroyed
     // until about:blank has loaded (which does not happen as long as the
     // element is hidden).
     this.browser.setAttribute("src", "about:blank");
     this.browser.docShell.createAboutBlankContentViewer(null);
 
     sidebarBroadcaster.removeAttribute("checked");
     this._box.setAttribute("sidebarcommand", "");
-    this._title.value = "";
+    this.title = "";
     this._box.hidden = this._splitter.hidden = true;
 
     let selBrowser = gBrowser.selectedBrowser;
     selBrowser.focus();
     selBrowser.messageManager.sendAsyncMessage("Sidebar:VisibilityChange",
       {commandID, isOpen: false}
     );
     BrowserUITelemetry.countSidebarEvent(commandID, "hide");