Your browser doesn't care about the extension of the file, only the content type that the server reports. (Well, unless you use IE because at Microsoft they think they know more about what you're serving up than you do). If your server reports that the content being served up is Content-Type: text/html, then your browser is supposed to treat it like it's HTML no matter what the file name is.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…