anonymity
which is why I said: “if security is the priority”
some people prioritize security lower than other things, and that’s their prerogative 
on a secure OS
Given how much of the average desktop use case is done in the browser, we have put and are continuing to put a ton of effort into browser hardening. There is no such thing as a “secure OS” independent of the browser, as far as the desktop use case is concerned. The security of your system is inherently tied to the security of how you interface with the internet. Using secureblue and ditching the browser hardening, userns hardening, etc is missing a good chunk of the point of secureblue.
Here’s a contrived example:
- A malicious website crafts a response payload that exploits a firefox/TB vulnerability in the CSS engine to escalate privileges
- since firefox/TB runs only with at most a weak sandbox, weak internal isolation, and no MAC confinement, the now compromised browser attacker scrapes your homedir info, network info, lan info, etc and sends it back to themselves
- The user is now significantly less anonymized than if they had simply used a browser that had measures in place to mitigate categories of vulnerabilities like this.
TLDR, using an insecure browser on a “secure OS” is contradictory, because of the criticality of the browser in the desktop use case.