Unable to access any site in FirefoxPortable - invalid error message received

This started occurring on my home PC (Windows10) on Friday 8 June 2018. When I fired up FirefoxPortable from my USB drive platform, and it opened my home tabs (office.com, google.com, wikipedia.org, and wiktionary.org), I saw the same result on each tab: "The owner of X has configured their website improperly. To protect your information from being stolen, Firefox has not connected to this website. The site uses HTTP Strict Transport Security (HSTS) to specify that Firefox may only connect to it securely. As a result, it is not possible to add an exception for this certificate."

Well, that would seem to be a total bullshit message. Microsoft, Google, and Wikipedia/Wiktionary have all configured their sites improperly? I don't think so. I tried going to Mozilla.org to see what information I could find on the error, but I got the same result there, too! So, here's what I've tried:

I deleted my profile folder under the Data folder and restored it from a backup taken a few days prior to this error. No change in behavior.

I uninstalled FirefoxPortable, downloaded the latest from PortableApps.com, and installed it anew. I.e. I had a nice, fresh, empty profile. Started FirefoxPortable. No change in behavior; still getting error.

I uninstalled FirefoxPortable again, downloaded again, installed again, and ran again. No change in behavior.

Now, this is where it gets super annoying. I have an install of PortableApps on my home PC's C: drive with several useful utility style apps installed underneath. I added FirefoxPortable to this install. Ran this Firefox. and no problem whatsoever.

It gets more annoying. I plugged in my USB at work, ran PortableApps, and ran FirefoxPortable. No problem, pages opened just fine.

So, this is only happening when I run FirefoxPortable from my USB drive when it is plugged into my home PC running Windows 10. But, if my home PC or its OS was the problem, then why would an install on the C: drive on that machine work without a hitch. If someone can help me resolve this, it would be greatly appreciated.