Javascript and Opera

I have been using the PHP interface with fckeditor, if in IE6 and Firefox you enter some javascript into the editor, submit the form and echo the $_POST variable the javascript is displayed to the screen as text. But if you do this with Opera 8.02 and view it in IE6, Firefox or Opera the javscript is executed, why does this happen? I can remove the script server side but would like the same behaviour as IE/Firefox since i would not like anyone executing javascript.