ChatZilla
I used to use ChatZilla back in 2004 when it was a little bit more buggy, and a bit less popular, when it was part of the original Mozilla Suite, which has been replaced by the oddly named SeaMonkey. However, the project has definitely grown since then.
The developers aimed to build an IRC client built using the current HTML, CSS, and Javascript standards. And they did just that. ChatZilla allows the users to style the client to their liking using CSS, just as you would with any website. You can also extend the program and add new functionality with Javascript and HTML.
As an IRC client it supports many of the same features as other IRC clients, but it’s conveniently runs from within your browser in a separate window. You can even run it in a tab (although there a few documented bugs when running it in that environment)
You can learn more about this project here. Or install it to FireFox by clicking the link below.
