Index: src/orca/Gecko.py
===================================================================
--- src/orca/Gecko.py	(revision 2378)
+++ src/orca/Gecko.py	(working copy)
@@ -2334,6 +2334,16 @@
            or (not len(event.source.role)):
             return
 
+        # We'll also ignore focus events on objects of role "unknown".
+        # This seems to be an indicator that Gecko has decided to
+        # discard an object on us.  See:
+        #
+        # http://bugzilla.gnome.org/show_bug.cgi?id=412677
+        # https://bugzilla.mozilla.org/show_bug.cgi?id=371955
+        #
+        if event.source.role == rolenames.ROLE_UNKNOWN:
+            return
+
         # We also ignore focus events on the panel that holds the document
         # frame.  We end up getting these typically because we've called
         # grabFocus on this panel when we're doing caret navigation.  In
