Pros
The only two pros of working at Mozilla are that it is fully remote and that the community still believes in the values that Mozilla has represented for years (internally, those values are vanished).
Cons
Whatever change or initiative you want to take, you have to go through a lengthy and waterfall approval process that will prevent you from delivering value in time for your customers (Firefox users generate revenues, so they are customers!). Higher-level management works completely isolated from the rest of the company. The only ones who are asked for an opinion when making a decision are those who are aligned on the operation model, business opportunity, etc. In a nutshell, they don't search for or listen to any divergent way of thinking. The VP and above are generally aggressive or passive-aggressive if you don't align with their thinking. Expect that questions they don't like just didn't get answered or that they interrupt you when reporting the status of a project giving you misleading and rude feedback in front of others. Of course, if you are aligned with them, they will cheer and be gentle because you are saying what they want to hear. The vast majority of engineers are spoiled and not used to working in a corporate environment. Don't ask for deadlines, commitments, or deep dives. Things are ready when they are ready. Teams fight against each other, blocking development until things are not done as they want. There is zero collaboration or cohesion unless they want to eliminate an outthinker. To get along, just wave and smile and underdeliver... there is always a good excuse for that.