Yeah, based on what you’re telling me now I’m almost certain they’re having the issue I referenced above.
In short, it stems from sites that used LetsEncrypt-issued certificates, where the root CA certificate that signed the web site’s cert was expired. That root CA cert expired on something like Sept. 30 and people all over the place started having issues with Chromium-based browsers, IF they were on older OSes (such as Windows 7) that either didn’t provide updates anymore, or if they had shut off auto-updates, etc. etc.
I can’t imagine your correspondent isn’t having issues with tons of sites. If they’re interested, they can look at this for solutions. For users encountering NET::ERR_CERT_DATE_INVALID Error
The site you linked uses the IXRG Root X1 CA, which is the typical replacement for impacted sites… lending even more probability to it being that issue.
Firefox and maybe a few other niche browsers were not affected because they install their own root CA certificate storage, rather than the operating system one.
Anyway moving on from there: glad you got it working. I used to use FireShot on Firefox and I remember it being excellent, it’s a good tool. The thing I like about the GoFullPage extension is that it doesn’t request any intrusive permissions, it’s pretty safe to have it installed and only use it when you need it; and until then it basically does nothing (and cannot because the permissions don’t allow it to).