You cannot add browsers to a factory created by others.
52.
In our dreams, the web looks good for all users. So we let web designers view screenshots of their pages in different browsers, at different screen resolutions and with different plugins.
Not everybody has a farm of legacy machines with older OSes and browsers. There are online services that offer screenshots of websites in different browsers for considerable fees. For the hobbyist and for open source projects, these fees may be prohibitive.