[nicbou]

Webkit was made to be embeddable, so it spreads faster. More webkit-based browsers exist.

Firefox as a project seems directionless. New releases anger its users with unwanted feature. Its custodians wasted so much energy on silly projects that people are reluctant to donate.

Oh and of course the competition comes pre-installed on millions of devices. Operating systems even remind you when you're not using their bundled browser.