You are getting this error message from Firefox 17 or higher when recording or replaying with Squish 4.2.x:
TypeError: netscape.security.PrivilegeManager is undefined
Firefox 17 and higher implemented significant changes to their API which broke compatibility with older Squish 4.2.x packages.
Please contact Squish technical support to obtain a recent Squish for Web 4.2 package. Please provide the file "<SQUISH_DIR>/buildinfo.txt"" as well so that our technical support knows right away which configuration you need.