I use Vivaldi, I don't know a better Chromium for privacy nor because other features (made in the EU by a employee-owned cooperative, no extern investors, gutted Chromium base (no phones to Google), no tracking, no logging, inbuild ad- and trackerblocker with customizables filterlists, encrypted sync, feed reader, mail client, calendar, reader list, reader view, splitscreen, full customizable UI, command chains, etc......). Apart with your account an own blogging platform, mail service, included an Mastodon account in the Vivaldis own instance, which you can use with your account. https://vivaldi.com

ungoogled-chromium

Ironically for Browser you shouldnt use Flatpaks if you trust the browser and you care about security.

https://madaidans-insecurities.github.io/firefox-chromium.html

What Distro are you on? I use Firefox and Brave, both as RPM now. I actually switched for convenience (keepassxc extension works, plasma extension works etc) but they are actually more secure.

Native Chromium is poorly way more secure than Firefox. When using the Browsers through Flatpak you need to remove the sandbox, so process isolation and memory stuff is gone, and replace the specific sandbox with bubblewrap.

Bubblewrap is good, but doesnt support isolated Tabs.

There are CSS exploits, but to my understanding just using Noscript in "block all by default" mode is best for security AND privacy.

I would like to like Brave, as it is more secure, but it sucks a lot. Very bloated, tab management worse, missing extensions, damn Chromium webstore and the addon not working so no updates. It is not bad, and I want to write a hardening config soon, to remove and disable all that bloat permanently.

I would not recommend Librewolf if you are advanced. For one it is a Flatpak, ironically (didnt know this a few weeks ago too) less secure. Also it lacks behind in updates a bit, not much, but this may become a problem.

https://github.com/trytomakeyouprivate/Arkenfox-softening

I am working on this tool, should work, that keeps your Arkenfox config up to date and sets a few switches to soften it. So you add that to Firefox and dont need Librewolf anymore.

On Fedora all you need is libavcodec-freworld from rpmfusion to get everything working. But ublue.it images work best out of the box.

Edit

Why are you downvoting this? Doesnt it fit your opinion? I also dont like Chromium, but its more secure. I also didnt know that Flatpak browsers are less secure, but thats a fact.

Why bother with such micro optimisations when the purpose is to be used extremely infrequently for compatibility reasons?