Index: src/orca/scripts/toolkits/Gecko/script.py
===================================================================
--- src/orca/scripts/toolkits/Gecko/script.py	(revision 4115)
+++ src/orca/scripts/toolkits/Gecko/script.py	(working copy)
@@ -5344,7 +5344,7 @@
                     if text:
                         newY = extents[1] + extents[3] / 2
                         newOffset = text.getOffsetAtPoint(oldX, newY, 0)
-                        if newOffset >= 0:
+                        if 0 <= newOffset <= characterOffset:
                             prevOffset = newOffset
                             prevObj = newObj
                     break
