A phoenix is born from the ashes of its past. Mozilla the browser was considered bloated by some and that led to a cleaner browser, a firebird if you will. This is just another indicator we're past due for another cycle of fire.
Starting from scratch doesn't have a chance at this point. The web is too complex for a volunteer team to build a brand new browser. So the only option is a fork of Firefox, but most of the people who have the time, energy, and ability to work on fully understanding the Firefox code base probably work for Mozilla.