All the hip kids are updating from RC1 to RC2.
update For those wondering why this is called Firefox 1.5 and not Firefox 1.5 RC2, it's because this is a genuine release candidate. The build you have, if not problems are found, will be Firefox 1.5. If we called it RC2 in the actual client, it wouldn't be a real release candidate because we'd have to make changes to the name and then create new builds.