Gone with DownThemAll! will be add-ons that e.g. let you change major bits about the Firefox user interface (e.g. tabs tree add-ons), add-ons that allow you to do more “advanced” stuff than just showing or slightly altering websites, such as e.g. restarting the browser upon click (unless mozilla kindly provides an API for that, which won’t be compatible with Chrome, of course).

I'm not ready to say goodbye to my tree tabs :'(