Bitdefender Free edition certificate "mess" in Firefox

Question

I have recently installed Bitdefender antivirus free edition on my windows 10 PC. All worked smoothly for several days. Then I saw this popup:

I was suspicious and the popup is still on my screen. When I Googled the words in the popup I found this SO question. It is clear that something bad is being attempted but I don't really understand what. Seeing the words in the answer "Bitdefender Free edition certificate mess" it seems that there is some fault in Bitdefender? Or Firefox? Or the interaction between the two?

And the line "Check if https://unsplash.com is hijacked and certified by BitDefender" is even more confusing. How could I tell if unsplash.com is "hijacked and certified by BitDefender". I am now nervous of even visiting unsplash.com.

Can anyone explain a bit of background to this problem?

EDIT: Please do not mark this as a duplicate of the original question - what I am asking is different. I already know the "solution" but what I am asking for is an explanation of why this is even a problem that needs to be solved.

Solution

it seems that there is some fault in Bitdefender?

You have configured BitDefender to scan your secure HTTP traffic. Enabling this option requires you to use a root certificate signed by Bitdefender in order to accomplish this task.

Or Firefox?

At this point, you have not installed the root certificate but you have also not disabled the Firefox extension Bitdefender likely installed. You need to either install the root certificate or disable the security feature.

How could I tell if unsplash.com is "hijacked and certified by BitDefender". I am now nervous of even visiting unsplash.com.

Allowing security software to break a secure connection between you and Google allows that security software (and in this case BitDefender the company) to intercept all data between you and Google and scan it.

Can anyone explain a bit of background to this problem?

The author is obviously is referring to issues like Superfish

The critical threat is present on Lenovo PCs that have adware from a company called Superfish installed. As unsavory as many people find software that injects ads into Web pages, there's something much more nefarious about the Superfish package. It installs a self-signed root HTTPS certificate that can intercept encrypted traffic for every website a user visits. When a user visits an HTTPS site, the site certificate is signed and controlled by Superfish and falsely represents itself as the official website certificate.