See also: IRC | Mozilla

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A basic IRC client that is fully cross platform and written entirely in JavaScript and XUL. You must be using a Mozilla-based browser to run ChatZilla. Originally a proof-of-concept chat device for Mozilla, it has continued to grow and develop, becoming a very useful and portable, albeit limited, IRC implementation. Mozilla still intends to produce a multi-network, all-inclusive instant messaging/chat tool like GAIM.

It now does support DCC file sending (see ChatZilla FAQ)

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