which standalone server to use

hi in my organization we use php for that i ahve downloaded stand alone server 2.20.0 and php unit , curl function and now i hjave a doubt that selenium stand alone server 2.21.0 should be used .. plz anybody can advise whether 2.20.0 or 2.21.0 standalone server is needed for me

you can use 2.20.0 server as you have already downloaded it.
I am also using same one..

k thanks much.. but in another forum they said firefox 12 supports standaloneserver 2.21.0 only...