fix XML parsing error

browser/locales/en-US/chrome/help/prefs.xhtml

@@ -472,7 +472,7 @@ Contributors:
   <p><em>Select new tabs opened from bookmarks or history</em><br/>When you open
     bookmarks or web pages from your browsing history in a new tab,
     &brandShortName; automatically selects the tab and displays the newly-opened
-    web page.  Uncheck this &pref.singular to load bookmarks and pages from your
+    web page. Uncheck this &pref.singular; to load bookmarks and pages from your
     browsing history in a background tab.</p>
 
   <p><em>Warn when closing multiple tabs</em><br/>When you close a window with