----- Original Message ----
> From: Noppanit Charassinvichai


> Dear All,
> I want to develop an extension that somehow it has to write a string to
> a xml file. How can I do that? because I have to save some kind of
> options that user chooses.


See http://developer.mozilla.org/en/docs...trees_to_files
for complete example


> Do I have to use XPCOM?


You have to use built-in XPCOM components. See http://developer.mozilla.org/en/docs...trees_to_files
You don't have to write your own XPCOM component.