Change http to https for client URLs, add +6697 for mibbit
There are several ways to participate in IRC and here are a some common options.
http://mibbit.com/ Mibbit]: web-based chat client.
* [https://kiwiirc.com/ Kiwi IRC] Open Source web-based chat client that works on mobile too.
* [https://addons.mozilla.org/en-US/firefox/addon/chatzilla/ Chatzilla] is an add-on for Firefox; it comes built-in with SeaMonkey. You can also install it [http://chatzilla.rdmsoft.com/xulrunner/ standalone].
http://konversation.kde.org/ Konversation] is a client for Linux, you can probably get it as a package from your distribution. Its look and feel is similar to that of ChatZilla while being built on [http://www.kde.org/ KDE].
http://colloquy.info/ Colloquy] is a Mac client with a nice looking interface. It also has a mobile client for iPad/iPhone/iTouch.
* [http://limechat.net/mac/ Limechat] is a cross-platform IRC client by Satoshi Nakagawa. Warning: main site is in Japanese, this is not just for Mac, there are [http://hp.vector.co.jp/authors/VA022249/files/lime218.exe Windows] and [http://limechat.net/iphone/ iOS] versions as well. A number of people have happily switched from Colloquy to Limechat.
http://www.mozilla.org/en-US/thunderbird/ Thunderbird] is a communication client made by Mozilla. As of version 15, it has IRC support.
* [http://www.instantbird.com Instantbird] is a cross-platform multi-protocol instant messaging client based on Mozilla technologies (and libpurple from Pidgin) with an emphasis on simplicity and extensibility.
http://www.yaaic.org/ Yaaic] is a free (as in freedom), multiserver, Android IRC client, now fully conformant with the UI style of the Iced Cream Sandwich (and later).
* [http://www.andchat.net/ AndChat] is a free (as in beer), multiserver, IRC app for the Android platform.
http://chat.mibbit.com/?server=irc.mozilla.org Click here to connect]
* enter a nickname for yourself, then click GO (no channel needed at first, but you can put one in if you know where you're going)
* look for a "Mozilla" tab right under the Mibbit logo and click on it (it doesn't come to the front automatically for some reason)