I have a few Linux servers at home that I regularly remote into in order to manage, usually logged into KDE Plasma as root. Usually they just have several command line windows and a file manager open (I personally just find it more convenient to use the command line from a remote desktop instead of directly SSH-ing into the system), but if I have an issue, I've just been absentmindedly searching stuff up and trying to find solutions using the preinstalled Firefox instance from within the remote desktop itself, which would also be running as root.
I never even thought to install uBlock Origin on it or anything, but the servers are all configured to use a PiHole instance which blocks the vast majority of ads. However, I do also remember using the browser in my main server to figure out how to set up the PiHole instance in the first place, and that server also happens to be the most important one and is my main NAS.
I never went on any particularly shady websites, but I also don't remember exactly which websites I've been on as root, though I do seem to remember seeing ads during the initial pihole setup, because it didn't go very smoothly and I was searching up error messages trying to get it to work.
This is definitely on me, but it never crossed my mind until recently that it might be a bad idea to use a browser as root, and searching online everyone just states the general cybersecurity doctrine to never do it (which I'm now realizing I shouldn't have) but no one seems to be discussing how risky it actually is. Shouldn't Firefox be sandboxing every website and not allowing anything to access the base system? Between "just stop doing it" and "you have to reinstall the OS right now there's probably already a virus on there," how much danger do you suppose I'm in? I'm mainly worried about the security/privacy of my personal data I have stored on the servers. All my servers run Fedora KDE Spin and have Intel processors if that makes a difference?
https://www.mozilla.org/en-US/security/advisories/mfsa2023-56/
That's a link to the most recent release of Firefox and the security vulnerabilities that were fixed.
You'll notice the first one listed says, "This issue could allow an attacker to perform remote code execution and sandbox escape."
So if you visited a site that exploited that bug, it escaped the sandbox and ran whatever code it wanted to. Since you were running as root it could do anything it wants. Your device is now the property of someone else. Potentially all your data has been stolen. You probably didn't even notice.
Now. Realistically. You probably didn't get exploited. Your device may not be vulnerable to that particular bug. But new bugs are found, and fixed, and created every day. Can you be sure you weren't exploited?
Let's look at it a different way. Think of it like driving a car with no seatbelt or airbags. As long as you don't crash, you're fine. The car still works fine without seatbelts and you have more freedom to move your arms around.
Let's look at it a different way. Do you ever lock the door to your home/apartment? Heck do you even close the door? Why not leave it wide open?
At the end of the day security is about layers and the trade offs for convenience. You can run KDE as root, and you can run Firefox as root. You'll probably be fine. It's like driving without a seatbelt or leaving your front door wide open, but you can do it. If you do drive with a seatbelt and at least close your front door, you can probably run KDE and Firefox as a regular user.