Per StatCounter, Mozilla's market share decline started in early 2010 (including mobile, late 2010 for desktop only) and Eich was fired (resigned, but that's BS) in early 2014.
Eich was still at Mozilla (not CEO) when Mozilla under-invested in desktop performance, failed to get Firefox OS off the ground, and most likely laid the groundwork to switching to Yahoo.
Mozilla bungled Firefox OS after I left, lost Andreas Gal and most of the top talent, lost Li Gong, while KaiOS based on same code and business plan, with some of the talent, took over and grew to over 200M phones. Blame Mozilla there.
I had nothing to do with the switch to Yahoo. That deal was a gleam in someone else’s eye and I left before it was done.
Last thing: how did not-me leadership do after I left, and I started Brave and grew it to 40M users while Firefox lost over 50M? You may dislike me, but your fantasy blame game cannot excuse Mozilla outcomes lately.