Firefox was even over 30% at one point. It's a fine browser, but that 30% was in the desktop era where the only competition was a stagnant IE.

Then mobile happened and Firefox failed to secure a seat at the mobile OS table. Nor does it have any big web property to push the browser. So neither on mobile nor on desktop does Mozilla have any leverage.

It's not an engineering problem, it's a leverage problem. But even in engineering Mozilla can't out-compete Google. There's no way out of this sink hole.

Such is the technical analysis, but I want to compliment it with the normie analysis: nobody gives a shit about browsers. They're free and all do the same thing. Hence people go with the default and stick to it for life.