Xtreix Firefox = more private is a persistent misunderstanding, this is not the case, Firefox is very behind in terms of security and privacy and is not innovating at all since a very long time
Xtreix Things like Site Isolation and state partitioning for network and storage first included in Chromium and more mature in Chromium are real features that improve security and privacy
I was under the impression that Chromium was lacking proper site state isolation, and that only Firefox had a proper implementation for that. At least a year ago. Ie, that Chromium has a shared cache for all top-level domains, and unless you disable third-party cookies, also share third-party cookies between top-level domains, making it trivial for one compromised site to detect what other sites you have visited (eg by requesting resources from other sites and measuring response time to see whether it hit cache or not). Whereas Firefox properly isolate all site state per top-level domain, ie each top-level domain has its own separate cache and cookie storage.
Has this changed recently?
Those are quite important privacy features, which were added only a few years ago to Firefox.
And then we of course have the anti-fingerprinting patch series from Tor Browser that has been uplifted to Firefox. Even if it isn't Firefox that developed it, it is today part of Firefox. At the same time, Chromium, including Vanadium fork, largely lack anti-fingerprinting resistance, since no one has developed any corresponding patch series for Chromium base.
As far as my understanding goes, it is still that Chromium has superior security, but Firefox has superior privacy.