Mozile can work side-by-side with other JavaScript in your pages. Of course, integration will take some extra work, and you'll need to know more about how Mozile functions than the average user. Here's some information to get you started.
The first step will be to remove the parts of Mozile that you don't need. If you have your own GUI, then disable the mozile.gui module. If you have your own system for saving, disable the mozile.save module. The section on packaging Mozile below has more details.
The second step will be to tell Mozile what to do. Our development documentation includes the full Mozile API, generated from the source code. Here are some of the methods you might be interested in.
mozile.execCommand(name, arguments...) - Execute a Mozile command. For the list of available commands see mozile.edit.allCommands.mozile.edit.enable() and disable() - These turn Mozile editing on and off throughout the whole document.mozile.save.save() and saveAs() - Use Mozile's save system.mozile.dom.selection.get() - Gets a cross-browser selection object which behaves like the Mozilla Selection object.