enable error reporting to the console with xulrunner 6

Hello

I m trying XULRunner 6 and I don't manage to get javascript errors 
(syntax, exceptions, etc) reported in the console/jsconsole.

My profile preferences are :
pref("browser.dom.window.dump.enabled", true);
pref("devtools.chrome.enabled", true);
pref("devtools.errorconsole.enabled", true);
pref("dom.report_all_js_exceptions", true");
pref("extensions.logging.enabled", true);
pref("javascript.options.showInConsole", true);
pref("javascript.options.strict", true);
pref("nglayout.debug.disable_xul_cache", true);
pref("nglayout.debug.disable_xul_fastload", true);

window.dump() works well, as does 
Components.interfaces.nsIConsoleService interface.
But Components.utils.reportError() does not work and JS syntax errors 
are not reported either.
My test sample is as shortest as possible : a single empty window and a 
loaded JS script file. I tried both i686 & x86_64 runtimes and I didnt 
find anything recently related in the bugzilla.

Here is the sample :

<?xml version="1.0"?>
<?xml-stylesheet href="chrome://global/skin/" type="text/css"?>

<window 
xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul" 
title="foo">
<script type="application/javascript" src="window-main.js"/>
<button label="click" oncommand="foo('click');"/>
</window>

the window-main.js contents is :
function foo(str)
{
     window.dump(str);
     Components.utils.reportError('error : ' + str);
     Components.classes['@mozilla.org/consoleservice;1']
             .getService(Components.interfaces.nsIConsoleService)
             .logStringMessage(('nsiconsoleservice : ' + str);
}
foo('startup');

The logged messages in the console (same for the jsconsole) are comes 
from window.dump() and nsiconsoleservice, but not from the reportError() 
function.
Did I forget something in my preferences ?