Loading an HTML file from disk using a specific encoding?

Hi all,

I have a XUL app that process some HTML files I have stored locally on
disk, loading them with browser.loadURI().

Is there a way I can define a default encoding when loading the file?

I have a few files, that I have encoded in utf-8, and they do not
contain a content-type declaration (specifying a charset). Opening
them with firefox, correctly detects that they are utf-8 files, but
doing the same in XulRunner (firefox -app), does not.

I have tried to set the charset in browser.loadURI(), but it has no
effect.