I'd be more inclined to use Firefox if it didn't feel so clunky, didn't keep trying to push Pocket on me, and took a more aggressive stance fighting against web annoyances and adtech.
Heck I might consider switching to Firefox if it could actually, reliably block autoplaying video - something that Safari and Chrome seem incapable of doing.
Browsers being:
1. massively complicated,
2. requiring massive feature support for compatibility with the ecosystem,
3. the biggest attack surface on anyone's computer, and
4. made by people doing huge amounts of work who want to eat.
I don't think we can have a secure, feature-complete, fully community-developed browser unless there's a massive refactor and simplification of HTML and related technologies.
Extensions had to be reworked. There was no way to make such implementation-dependent code stable for each release. The current API is much more limited in scope as well, but the performance and security concerns were and still are very valid.
I'm not a fan of the new tab page, and I have generally disliked how the settings have been reworked, but I still think then end product is better than Chrome.
(On the other hand, Opera 12 was the king of resource usage...and I miss it)