Hi Neil

I'll try your way too. Again Thanks a lot :)
Also found a way myself which seems to work:

I found the solution. Just need to get the Parent windows of the one I
wa using. Except if you want the "unload" event which seems to only
work for the window I was first using. Here goes the complete updated
code for those who might have had the same troubles as I.
Thanks again to Neil for his great help.

void CSpecialThing::getBrowserQuestionForForum()
{
    nsString wsHrefXul      = NS_LITERAL_STRING( "chrome://xulcrawler/
content/main.xul" );
    nsString wsIDBrowser    = NS_LITERAL_STRING( "mybrowser1" );

    // --- A lot of variables ---
    nsresult rv;
    nsCOMPtr<nsIDOMWindowInternal>      pWinInt(0);
    nsCOMPtr<nsISimpleEnumerator>       pWinEnumerator;
    nsCOMPtr<nsIDOMLocation>            pDOMLocation;
    nsCOMPtr<nsIDOMWindowCollection>    pDOMWindowCollection;
    nsCOMPtr<nsIDOMWindow>              pDomWin;
    nsCOMPtr<nsIDOMWindow>              pDomWinBrowser;
    nsCOMPtr<nsIDOMDocument>            pDomDoc;

    // -----------------------------
    // --- Get DomWindowInternal ---
    // -----------------------------

    nsCOMPtr<nsIWindowMediator>
pWindowMediator(do_GetService(NS_WINDOWMEDIATOR_CONTRACTID));

    nsString sWindowType( NS_LITERAL_STRING("") );
    rv = pWindowMediator->GetEnumerator( sWindowType.get(),
getter_AddRefs(pWinEnumerator));

    PRBool bHasMoreElements;
    rv = pWinEnumerator->HasMoreElements( &bHasMoreElements );

    while ( bHasMoreElements ) {
        nsCOMPtr<nsISupports> pSupportsWin;
        rv = pWinEnumerator->GetNext( getter_AddRefs(pSupportsWin) );
        nsCOMPtr<nsIDOMWindowInternal>
pWinInternal(do_QueryInterface(pSupportsWin));

        rv = pWinInternal-

        nsString wsHrefTest;
        rv = pDOMLocation->GetHref( wsHrefTest );

        // See if we have the correct (XUL) URI
        if ( wsHrefXul == wsHrefTest  ) pWinInt = pWinInternal;

        rv = pWinEnumerator->HasMoreElements( &bHasMoreElements );
    }

    // --- Get the "mybrowser1" element ---
    pWinInt->GetFrames( getter_AddRefs(pDOMWindowCollection) );
    pDOMWindowCollection->NamedItem( wsIDBrowser,
getter_AddRefs(pDomWin) );

    pDomWin->GetParent( getter_AddRefs(pDomWinBrowser) );

    // --- Add events ---
    nsCOMPtr<nsIDOMEventTarget>
pDomEventTargetBrowserWin(do_QueryInterface(pDomWin));
    nsCOMPtr<nsIDOMEventTarget>
pDomEventTargetBrowser(do_QueryInterface(pDomWinBrowser));
    pDomEventTargetBrowser-

PR_FALSE);
    pDomEventTargetBrowser-
    pDomEventTargetBrowserWin-

    // ---------------------------------------------------------------
    // --- Bonus example on how to get the current URI of the page ---
    // ---------------------------------------------------------------
    pDomWin->GetDocument( getter_AddRefs(pDomDoc) );
    nsCOMPtr<nsIDOMDocumentView>
pDomDocumentView(do_QueryInterface(pDomDoc));
    nsCOMPtr<nsIDOMAbstractView> domAbstractView =
getDefaultView(pDomDocumentView);
    nsCOMPtr<nsIWebNavigation>
webNavigation(do_GetInterface(domAbstractView));
    printf("webNavigation uri: %s\n",
getCurrentURI(webNavigation).c_str() );