Right now, Firefox's strategy seems to be focused on trying to follow in Google's footsteps and do everything they can to implement something almost as good as Chrome just without some--but not all!--of the extra things we hate about Google. The result of this strategy is there are simply way too few answers to the question "why should I use Firefox instead of Chrome?" that aren't "because someone has to lest we lose the war, and it may as well be you (as I guess you drew the short straw today)" :(.
I want to be clear: these unique selling propositions can be really small. If you are using Linux on a computer with a touch screen, Firefox implemented good multi-touch with kinetic scrolling support for X11... it puts Chromium to shame, and so if you are using such a computer you are likely to use Firefox even if it is less performant or doesn't work with a few websites you like. The goal isn't to only target the majority by chasing analytics: it is to win a thousand 0.01% minorities that add up to 10%.
The only other UI thing--and I'm using Firefox right now, and have been using Firefox as my primary browser for months now--that I can think of are container tabs. This one is interesting because, frankly, it doesn't buy me that much over Chrome's support for multiple profiles, and yet I do slightly prefer the feature, and clearly a bunch of other people do if you look around: implementing this feature won Firefox a bunch of users who now consider this part of their workflow and can overlook other faults.
Firefox used to be really good at this: they owned the space of web developers due to Firebug--which was also a critical market as it meant websites tended to work in Firefox--but Chrome saw that and took it from them. If I were in charge of Firefox, my hail marys wouldn't be allocated to end user acquisition: it would be focused on what I can offer developers to get them back to using Firefox as their primary browser. But like, it isn't even clear to me Firefox right now cares about developers anymore :/.
I mean... not only did they lay off the entire MDN writing team back in 2020--which to me was putting Firefox at the forefront of developers' minds (in the same way you mention users knowing about Google)--but, as far as I understand, they also laid off a lot of the dev tools team. Their website showing the features of Firefox for developers sounds strong, but I feel like Chrome also now has all of this stuff. I am excited to see that Firefox claims to have better support for CSS Grid debugging, I guess?
I also say that, because another place Firefox used to have a unique selling proposition is that it was "the hacker's browser": you could easily alter any part of the interface due to its crazy XUL layer, and I knew a ton of developers and users alike who would sell you on Firefox due to the crazy Firefox-specific extensions you could install. But as Chrome added extension support, Firefox not only wanted to be compatible with Chrome's extensions... they dropped (almost) everything that was unique about Firefox.
As it stands, they at least do retain some functionality that isn't just the same as what Chrome offers: support for synchronous fetch hooks (which I might be describing poorly) that is used by the more advanced ad blockers. This is a great USP because, of course, Google isn't going to support those... but Firefox stops there. I contend that it wouldn't be a big lift for them to add some extra Firefox-specific extension API surface and get, for example, the Tridactyl user community back to 100% on Firefox.
And there is frankly a ton of uncharted territory on being able to make powerful web extensions. I used to be in charge of the iPhone native code extension community, and I seriously feel more crippled trying to easily modify a web page than I ever did with a native Objective-C app, and that's insane: I myself constantly run into roadblocks due to being unable to dig into the private data of JavaScript objects or closures, and I see other developers complain about being locked out of styling web components.
Firefox should lean into "it is easier to hack the web with Firefox" as we know Google is going in the opposite direction. Despite the insane complexities of jailbreaking your iPhone, we had around a consistent ~10% marketshare; and no: that wasn't piracy! Not only did the US Copyright Office investigate and say we weren't the problem, we had a thriving ecosystem of paid native app extensions! (Though, frankly, if Firefox managed to hold ~10% marketshare entirely on the back of piracy, I'd be OK with that!)
Otherwise, as it stands, Firefox seems to be removing unique selling propositions as they focus on narrowly re-implementing exactly the set of things offered by Chrome. They have decided that the only market worth targeting is the mass market, and so they are making the same analytics-driven decisions Google makes with respect to safety, streamlining, and prioritization that forsake developers and power users as part of a losing battle with Google for 90% of the web when they used to own the other 10%.