Firefox's market share peaked in 2009. Eich was CEO for 2 weeks in 2014. He resigned and declined Mozilla's offer to remain in another C level position. The same lawyer lady Mitchell Baker had every top job from 1999 to 2008.
At this point I think it's clear his resignation was not voluntary. Maybe the other offer was sincere, or maybe it wasn't; I'm not sure how we could tell.
You seem awfully eager to assert something false, possibly out of bad conscience. No one involved in my departure had a good solution for my staying at Mozilla, including me.