What is Chatzilla?
Discontinued since 2017. From their website: “With the release of Firefox 57 (Firefox Quantum), it is no longer possible for ChatZilla to work as an extension in Firefox.”
Comments and Reviews
Said about Chatzilla as an alternative
While not a drop in replacement, ChatZilla is lighter and installs as a browser add-on.
It is HTML5 based and will run on any platform that has a Mozzila-Based Browser that uses XPI extensions, such as Firefox. (This includes several Mobile platforms.)