Read [http://kb.mozillazine.org/Unable_to_install_themes_or_extensions_-_Firefox#Unexpected_installation_error_-203 Unexpected installation error -203]<br /> Reset extension files; see [http://kb.mozillazine.org/Unable_to_install_themes_or_extensions_-_Firefox#Corrupt_extension_files Corrupt extension files] '''If this reply solves your problem, please click "Solved It" next to this reply when <u>signed-in</u> to the forum.''' ------------------------ Not related to your question, but... You need to update some plug-ins: *Plug-in check: https://www-trunk.stage.mozilla.com/en-US/plugincheck/ *Adobe Shockwave for Director Netscape plug-in: [https://support.mozilla.com/en-US/kb/Using%20the%20Shockwave%20plugin%20with%20Firefox#w_installing-shockwave Installing ('''''or Updating''''') the Shockwave plugin with Firefox]