Before Caret in Firefox

Hi everyone,
I'm developing a plugin for FCKeditor 2.6 version integrated in Mediawiki .
I need the equivalent of above code in firefox (and Googole ChromeChrome) for return me alls html text in textarea before the caret position.
I accomplished it in IE with this code:

   
   if (FCK.EditorDocument.selection) 
      {
      var Sel = FCK.EditorDocument.selection.createRange();
   
      Sel.moveStart ('character', -1);
      Beforecaret = Sel.htmlText;
      }

I need it this to select (if exists ) a particolar template before caret on press backspace key.
Any Idea?

Thanks in advance for help