diff --git a/toolkit/content/widgets/browser.xml b/toolkit/content/widgets/browser.xml
index 5dd159840f9c..3578f928b85d 100644
--- a/toolkit/content/widgets/browser.xml
+++ b/toolkit/content/widgets/browser.xml
@@ -702,6 +702,9 @@
           
           this._fastFind = null;
           this._webBrowserFind = null;
+          
+          // The feeds cache can keep the document inside this browser alive.
+          this.feeds = null;
 
           this.removeEventListener("pageshow", this.onPageShow, true);
           this.removeEventListener("pagehide", this.onPageHide, true);