Recheckin bug 271348 ('Move system caret with focus/selection changes' needs to explain that this is the same as caret browsing)

browser/components/help/locale/en-US/prefs.xhtml

@@ -410,11 +410,12 @@ Contributors:
     people.</p>
 
   <h3 id="accessibility">Accessibility</h3>
-  <p><em>Move system caret with focus/selection changes</em><br/>Specifies
-    whether to move the system caret whenever the focus or selection changes.
-    Some accessibility aids, such as screen readers and screen magnifiers, use
-    the system caret to determine which area of the screen to read or
-    magnify.</p>
+  <p><em>Move system caret with focus/selection changes</em><br/>Also known as
+    Caret Browsing, this specifies whether a moveable cursor is displayed,
+    allowing you to select text with the keyboard. Some accessibility aids, such
+    as screen readers and screen magnifiers, use the system caret to determine
+    which area of the screen to read or magnify. You can toggle this mode by
+    pressing F7.</p>
 
   <p><em>Begin finding as you begin typing</em><br/>When this &pref.singular; is
     enabled, &brandShortName; will find within the current web page what you