Pros
Competitive base salary and strong cash bonus (no stocks, however) plus the occasional performance bonus (also cash). Company all-hands several times a year in exotic locations (Orlando, London, Hawaii). It's like 2-3 extra vacation weeks a year, all expenses paid. At the last one I didn't attend any of the sessions and nobody noticed or complained.
Cons
I don't know where to start. I love the mission but the place is like train wreck in slow motion ever since Brendan Eich left. The new CEO is clueless and incompetent. He's widely ridiculed inside the company even by senior management. Most of the executives are just hiding and collecting their paychecks. Over the last 2 years the company has given up on Firefox OS and is giving up on mobile in general now to focus on the desktop browser, which fewer and fewer people want to use.