Which came first, Amazon or Facebook?

Amazon came first, by 10 years. Jeff Bezos incorporated the company in Washington state.

Side by side

Amazon

Amazon was incorporated on 5 July 1994, originally as Cadabra, and the website opened in July 1995 selling only books. The 1994 incorporation date is used here because it is the company's own founding date; if you mean the shop, 1995 is the answer. Either way it predates Google by three or four years and eBay by about a year.

Facebook

Facebook launched on 4 February 2004 restricted to Harvard email addresses, opened to other universities through 2004 and 2005, and to anyone over 13 with an email address in September 2006. It is six years younger than Google and a year older than YouTube. Its predecessor Facemash, which compared students' photographs, was shut down by the university within days in 2003.