Hi, and welcome to JustAnswer! My name is XXXXX XXXXX I am excited to get started with you.The reason why you are not able to update firefox or Safari is because you are running an unsupported operating system. Newer versions of safari and firefox are only available on macs running 10.6 or higher. You can purchase 10.6 here http://store.apple.com/us/product/MC573/mac-os-x-106-snow-leopard
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