They are of course highly relevant for their user bases, but in terms of "browsers that might break the Chrome hegemony through normal competition", there are none. You'd need to pull a Microsoft IE-on-Windows on Google and enact laws that forbid them from loading Chrome as default and only browser on all first and third devices associated with their brand. A few administrations ago, that might have still been a possibility, but it's not going to happen unless the EU does it first, and even then, the US might pull one of those idiotic "how dare the EU punish a US company for outcompeting everyone else" and instead enact reactionary laws that loosen the rules for them instead.
How about actually just making a good, competitive browser instead? Firefox is not failing because of Google's monopoly; it is failing because as a product it is unable to compete and beat Chrome where it matters. If not Mozilla, I am pretty sure somebody else will make such browser (and search engine, and email... ) eventually.
There is no "just". There is so very much no "just" anywhere near this topic.
There are a number of good options, but very few that don't further cement Google's control over the world's browser-engine code.
(Yes, I know there are some other very minor players that lag behind on features and standards support. I don't think that's what the parent commenter is looking for.)