Nope, the embedded Mibbit does not support the /list command. Which is annoying and dumb, but the way it is.
Most of the channels on the server (especially those with more than 10 members at any given time), aside from the #swc- channels, are for factions. Check with your faction, they may have a good channel to hang out in.
If you are foreign, there are also channels for different nationalities (#german, #spanish, #nederlands, #aussie, etc).
Public channels (aside from the large #swc- channels, which I've hidden to prevent spambots from flooding them as we've previously had issues with that) can be seen at this SearchIRC link for browsing.