If you click the "Technical Details" section of the page, does it contain this error code:

• sec_error_untrusted_issuer

In that case:

A common problem recently is Firefox not being set up to work with your security software. Some security suites include a filtering feature. In order to filter secure connections (HTTPS URLs), the security software presents a fake certificate to Firefox so it can intercept and stand in the middle of the secure connection. To have Firefox trust these certificates, you may need to do something such as import a root certificate, or click something in your security software's settings.

Of course, the problem also could be caused by spyware.

If you have added Exceptions, please check the "Issued by" section on one or two of the exceptions you've made to learn more about the source of this issue.

orange Firefox button (or Tools menu) > Options > Advanced > Certificates mini-tab > "View Certificates" button > Servers tab

Click a certificate and use the View button. The kind of issuer you might find is:

• Name associated with your security software, such as ESET, BitDefender, etc.
• Sendori (indicates unwanted software from Sendori)
• FiddlerRoot (indicates unwanted software named similarly to BrowserSafeguard, BrowserSafe, SafeGuard)
• Something else

If you have not added Exceptions, you can click the Add Exception button in the error page, then in the dialog click View Certificate or Get Certificate to see the Issued by section. You do not need to finish adding an exception.

What do you see?

I see this, I also went through my certificates and deleted those that were "no longer trusted"

Aha, Sendori.

If you go into Control Panel, Uninstall a Program, and sort by date (click the "Installed on" column heading) can you associate it with anything else? Trying to figure out how it gets on peoples' systems (i.e., bundled with some freeware?).

Oh, by the way, there are some "do not trust" entries built into Firefox that will reappear on the Servers tab after you exit and restart it. These invalidate some known bad certificates from a few years back that could possibly still be out there on some servers.

should I delete Sendori? The only stuff I could think of is Utorrent, I have a good amount of games but all through a trusted third party... What should I do to help you figure this out? Would you like a picture of the program list? And also thanks so much for your help!

yes, uninstall sendori - that is just useless adware that is intercepting all your network traffic. you might also want to run a full scan of your system with different security tools like the free version of malwarebytes and adwcleaner to make sure that adware isn't present in other places of your system as well.