Vantaggi
Mozilla has an outsized influence on the web and technology in general. If you want to build a web that is fair and just for all, this is a great place to do it. The engineering talent here is second to none. A large fraction of its employees work remotely, either from home or at coworking locations. As a remotee, you always feel connected to your team, because you're not a "special case". In fact, I feel more a "part of something" here than I have at jobs where I've had to drive to an office every day. It is also fantastic for work life balance: the flexibility means I can give to my family and not feel like I'm not giving work short shrift.
Svantaggi
Writ large, the company as a whole can feel a little directionless at times. If you're self-motivated and a self-starter, you'll do well, but you need to be flexible to adapt to changes and drop projects you may have grown attached to.