A rolling release means a continuously developing software system,
while most Linux distros have versions, that will be
replaced by new versions regularly, mostly about twice a year.
Rolling releases based on the Debian repositories on
live CD or live DVD are
Aptosid, which replaced the former Sidux, which is using
Debian "Sid", look at
an upcoming new release has been announced:http://aptosid.com
and the new Linux Mint Debian, based on Debian "Testing", at
"Sid" and "Testing" are the branches of Debian containing
more recent software developments, which are not in the
so-called "Stable" branch of Debian yet. Debian is the
base of many other distros like Ubuntu or Mint.
Security updates in Debian are generally not made by
installing newer software versions, but by fixing the
bugs in the existing older versions.This does also
include browsers like iceweasel and iceape (renamed from
Firefox and Seamonkey) or iceape (Thunderbird).
Fixing the bugs of the older versions instead of using
new versions is supposed to increase the stability
of the Linux system.
May be worth to have a look at, if you want something
a bit different from the usual path.