I want to use the web browser Epiphany as a secondary browser, but Windows Live Mail won't let me log in using this web browser. For that reason, I want Epiphany to identify itself as another browser, e.g. Firefox. Is this possible?
No, unfortunately, epiphany doesn't support masquarading itself as another browser. If you would like a browser with this capability, Midori is a nice lightweight web browser that supports disquising itself as other browsers. Hope that helps!