src/main/java/org/efaps/ui/wicket/components/modalwindow/ModalWindowContainer.java
@Override
    public ModalWindow setInitialWidth(final int _initialWidth)
    {
        int width = _initialWidth;
        final WebClientInfo wcInfo = (WebClientInfo) getSession().getClientInfo();
        if (wcInfo.getProperties().getBrowserWidth() > 0 && wcInfo.getProperties().getBrowserWidth() < _initialWidth) {
            width = wcInfo.getProperties().getBrowserWidth();
        }
        return super.setInitialWidth(width);
    }
@Override
    public ModalWindow setInitialWidth(final int _initialWidth)
    {
        int width = _initialWidth;
        final WebClientInfo wcInfo = (WebClientInfo) getSession().getClientInfo();
        if (wcInfo.getProperties().getBrowserWidth() > 0 && wcInfo.getProperties().getBrowserWidth() < _initialWidth) {
            width = wcInfo.getProperties().getBrowserWidth();
        }
        return super.setInitialWidth(width);
    }
Check it the size of the modal window is not to big and reduces it if
necessary.

@see org.apache.wicket.extensions.ajax.markup.html.modal.ModalWindow#setInitialWidth(int)
@param _initialWidth width
@return this Modalwindow