TinyMCE Draws Okay, But Won't Let Me Type In It. In FF, Buttons Have Error: Component returned failure code: 0x80004005

Error: [Exception... "Component returned failure code: 0x80004005 (NS_ERROR_FAILURE) [nsIDOMNSHTMLDocument.execCommand]"  nsresult: "0x80004005 (NS_ERROR_FAILURE)"  location: "JS frame :: http://mysite/tiny_mce/tiny_mce.js :: anonymous :: line 1"  data: no]
Source File: http://mysite/tiny_mce/tiny_mce.js
Line: 1

<script type="text/javascript" src="http://mysite/tiny_mce/tiny_mce.js"></script>
<script>
tinyMCE.init({
    mode : 'none',
    editor_selector: 'mceAdvanced',
    theme : 'advanced',
    theme_advanced_toolbar_location : 'top',
    theme_advanced_toolbar_align : 'left',
    theme_advanced_buttons1 : 'fontsizeselect,bold,italic,|,bullist,numlist,|,outdent,indent,|,removeformat',
    theme_advanced_buttons2: '',
    theme_advanced_buttons3: '',
    theme_advanced_font_sizes: "1, 2, 3, 4",
    width: '600',
    height: '200',
    remove_script_host : true,
    cleanup_on_startup : true,
    cleanup: true,
    debug : true,
    convert_urls : false
});

tinyMCE.execCommand('mceAddControl', true, 'fldOverview');
</script>

<textarea id="fldOverview" name="fldOverview" class="textbox"><?= OVERVIEW ?></textarea>