The Firefox market share was eaten largely by the enormous and legally dubious marketing campaigns by Google and Microsoft. Hard to see how Mozilla could compete with constant forced nags and defaults in the most widely used websites and operating systems.
The Firefox market share was eaten by being worse than Chrome, especially around the developer tools and extensions market places at the time.
No, Chrome was genuinely better than Firefox back then. Firefox didn't have multiprocess until many years later and Flash constantly crashed the browser.
It was a big factor, but so were things like the way they treated their mobile browser for years and years, which is the platform 2/3 of browser traffic now originates.
According to statcounter's stats, Firefox never cracked 1% of monthly mobile traffic any month from when stats started in 2009. Even Opera and UC have more than double Firefox's average for the last year and they are just Chromium forks users are downloading off the stores.