How to change cursor position

[Alex Furman]

Hi, I'd like to add some additional HTML text at the end of a mail in
thunderbird's "compose" window.
I can use the following code

var editor = gMsgCompose.editor;
var html_editor =
editor.QueryInterface(Components.interfaces.nsIHTMLEditor);
html_editor.insertHTML(messageText);

There is only one problem. This code inserts HTML text at current
cursor position,
but I need it at the end of a mail. Actually I have to move cursor at
the end of a mail before call previous code.
But I have no idea how to move a cursor. Could anybody help me?

Best regards, Alex Furman