ChatZilla Plugins
Shows a tree for your server, channel, and private message views. With the tree you can see activity in channels and servers, part, disconnect, toggle whether to connect/join on start up, just like with the tabs. Unlike tabs, when you open many channels, their names won't be squished into one unintelligible horizontal row.
Zip the plugin directory, use ChatZilla's "Install Plugin" menu, and select the zip.
Place plugin directory in chatzilla/scripts in your ChatZilla profile directory. You should end up with the following file structure:
<home directory> └── .chatzilla └── xxxxxx.default └── chatzilla └── scripts └── <plugin directory> ├── init.js └── <other plugin files>