Firefox rolls out Total Cookie Protection by default to all desktop users worldwide | It is Firefox’s strongest privacy protection to date, confining cookies to the site where they were created
Updated Aug. 28, 2024. Take back your privacy Firefox is rolling out Total Cookie Protection by default to more Firefox users worldwide, making Firefox the
making Firefox the most private and secure major browser
If calling home and to selected 3rd party analytics aren't part of the metric then yes, Firefox might be the most private. What proof, even they say they've telemetry.
But it's not a "major browser." It's a niche fork that has valuable adjustments for power users, but would be unusable for your average non-technically inclined user. I use Librewolf myself and appreciate it, but it's not something you can just drop on an older relative's machine and expect to work fine. Firefox has plenty of issues out of the box with sneaking in ads and telemetry, but at the same time you still have to understand that it's an important player in the market despite its flaws because it's the only real mainstream competitor to an entirely Chromium-based ecosystem, and despite the issues it does have, it's still lightyears ahead of Chrome.