Web client works on GlassFish 4, but not on GlassFish 3

Web client works on GlassFish 4, but not on GlassFish 3

I'm developing some enterprise web site using Java EE 6 technology. My
collegue was assigned working on web client and he develops it on his PC
using JSF 2.1 and GlassFish 4.0. When I tried running that web client on
my PC, which at first had GlassFish 3.1 instaled, it didn't work. Not a
single line of xhtml code was rendered on my web browser.
Later on, I installed GlassFish 4 and deployed application on it and look
at miracle - it worked! So basicaly, my question is simple: Why does that
happend? Why can't I run web client on older version of GlassFish server?
P.S. No error or warning is recorded on server's log when I try to run it
on GlassFish 3.1.