And a much less feature complete: https://github.com/nickdesaulniers/fxos-irc (100% client side, no websockets proxy or such)

or better:

http://firessh.net/ (add-on)

Another open source alternative https://kiwiirc.com/ (but it doesn't yet have persistence built in)

Glad someone mentioned this. The creator DJ put a lot of work into this, and it works very well.

i wish it could send push notifications to my phone.