I solved my Norton woes about 20 years ago. I uninstalled it and let my subscription lapse.

Let me translate that interesting bit of marketing lies.

Thunderbird does not trust the self signed encryption certificate used by Norton. Legitimate server operators pay for a legitimate certificate from a certified CA. See this Wikipedia article https://en.wikipedia.org/wiki/Certificate_authority

Thunderbird uses certificates issued by trusted certifying authorities. Becoming a public Certificate Authority (CA), you must establish a robust Public Key Infrastructure (PKI) that meets strict security and policy requirements, including technical infrastructure, physical security, and operational procedures. You will then need to apply to web browser and operating system developers for inclusion in their trusted root store, a process that requires individual applications and adherence to browser-specific programs.

Norton have not done that, so users are required to manually suborn the entire trust network created to validate encryption certificate as legitimate and manually add Norton as a certifying authority. There is nothing intrinsically wrong with doing that if you implicitly trust Norton. But remember that are a company incorporated where? They are co-headquartered in both Prague, Czech Republic (EU) and Tempe, Arizona (USA). So I guess by implication you are also trusting both governments not to require release of your information as well. There is much talk about Chinese companies and personal information, the reality is all national governments can compel companies under their jurisdiction to release just about anything. It is only a matter of making a law.

I use windows defender and it does not scan mail thus neatly side stepping the issues of encrypted connections. But Microsoft can issue their own certificates and do not meddle in mail. This is something I find interesting really, that those that already can don't choose not to, yet those that do not have the authority are seeking ways to do so.

BTW instead of taking photos on a device that results in something that appear on it's side and is very hard to read you might want to consider using screen shots instead.

See https://support.mozilla.org/en-US/kb/how-do-i-create-screenshot-my-problem#w_create-a-screenshot-on-windows you will need to ignore the Firefox screenshot information, but the use of the print screen keyboard button is not application specific.

I have this problem too. It began a couple of days ago. Note: you can NOT take a screenshot of the popup nor can someone remotely accessing your computer see it. I know that Norton sometimes makes it impossible to see their popups, which is why a photo taken from a phone is the only way to show the popup to someone. I spent hours on Norton's tech support and they have currently given this to their senior tech team to investigate. I'm waiting for a response. The "Resolve" button does nothing. Thunderbird already has the certiciates that Norton says it needs. Norton's uninstall/reinstall tool also does not resolve the issue. This is not something that has been a problem in the past. Norton must have done something.

The common thread here is Norton. Have you contacted them for support with the software you are paying for that is placing mindless messages on your screen? What was the result?

I have over the years learned you have to screenshot or copy Norton support pages as anything that is damaging to the corporate reputation has a very short shelf life when returning or referencing the information later the page just does not exist. They have a habit of purging their support site on a fairly regular basis so faults in one version that are not fixed in the next are not obvious.

I contacted Norton twice, although very courteous and patient, they were very unhelpful. I think they have no idea what to do either. Screenshots of Norton pop-ups seem to be blocked, so I had to take a photo. The photo is upright on my phone and pc, so something is happening to it when it is uploaded that is turning it on its side.

Not a permanent fix, but you can get rid of it for a while by temporarily disabling all notifications. Not ideal but at least I only have to wack the mole once a day.

to Matt - moderator: As I expalined, you CAN NOT take a screenshot of this popup. It simply does not work. I know how to do that and tried several ways, it just doesn't show up on the screenshot.