I agree, but to be fair, software usability often experiences death by a thousand UX cuts, and gnome-keyring support is one of those cuts. I don't think that's the case with web browsers, though. for the most part, things that matter
do just work, both in Firefox and Chrome.
The things I suspect could make a difference to Firefox marketshare are performance and transformative features.
For performance, UI latency needs to be near-zero to make it feel snappier than Chrome, and JS- and CSS-heavy pages noticeably faster than in Chrome. (Yes, pages shouldn't be so JS- and CSS-heavy, but they are, and users don't care that it's the web developers' fault. The browser that solves that problem wins.)
For features, tabs are one clear example, as were blocking popups, and session restore. Containers, adblock, Pocket integration, and Reader Mode all seem like they could have been this, but they weren't. Big features will be hit-or-miss, and will quickly be copied, but possibly a big deal for a short while.
Perf, of course, is a lot of hard engineering work, and features may be as well, in addition to being potential duds. Things like gnome-keyring feels like a relatively simple quick-win, despite being very low value compared to various other possibilities.
Personally, I thing I switched back to Firefox when they made restarting it when you have a hundred tabs retain the tabs, but not load them until you switch to them. That moved restarting the browser from a big deal to something I can just do whenever. (It was also when Quantum/Servo stuff was happening, but I think it was the tab thing that got me.)