I guess you mean supported browser for frontend editor, right?
Not an official list, and no official committment, but we try not to
break IE 8 (I don't thing anyone tested it on older version of Explorer).
Any reasonably recent version (less than two years) of the other
browsers is fine.
FinalAngel might have a better insight on this topic, though
--
Saluti
Iacopo Spalletti