Sabayon is similar to gentoo in that it uses portage for package management.. portage compiles programs from source (with a few exceptions for large programs, such as firefox, which both a source and a binary are available). Thus programs are ---compiled--- to better suit your system, unlike other linux distributions which are mostly binary and thus programs are made for a generic (slower computer) environment. Thus, in comparison to other distros, package management is "slow". If you do not want to deal with the wait time in exchange for stability and speed when the programs are installed, sabayon is not going to be a good distro for you. Go with a binary such as ubuntu, pclinuxos, mepis, whatever, or wait some time for entropy on Sabayon to be finished.
As for firefox, you will need to (in konsole as root or with sudo) emerge mozilla-firefox-bin or get it from portato similarly. That is the precompiled binary of FF 126.96.36.199 if I'm not mistaken, and thus will not take very long, whereas some people say compiling firefox (emerging mozilla-firefox as opposed to mozilla-firefox-bin) would otherwise take hours to compile.