The weirdest was a co-worker who had some simple webserver, which was listening on only IPv4 or IPv6 (but not both). When he went to "localhost" on Firefox it u

The weirdest was a co-worker who had some simple webserver, which was listening on only IPv4 or IPv6 (but not both). When he went to "localhost" on Firefox it used IPv4 and he was able to see it. On Chrome "localhost" was IPv6 (or the other way around), and he got "Could not connect" error. It confused him no end how this simple web server worked on FF but not Chrome. :)