What's your computer system and Firefox version?

There is security software like Avast, Kaspersky, BitDefender and ESET that intercept secure connection certificates and send their own.

https://support.mozilla.org/en-US/kb/firefox-cant-load-websites-other-browsers-can

https://support.mozilla.org/en-US/kb/firefox-and-other-browsers-cant-load-websites

https://support.mozilla.org/en-US/kb/secure-connection-failed-error-message

https://support.mozilla.org/en-US/kb/connection-untrusted-error-message

Websites don't load - troubleshoot and fix error messages

http://kb.mozillazine.org/Error_loading_websites

I using Ubuntu 18 and Firefox vs. 68 and there is no security software but this is only happening in Firefox not in chrome,opera, safari browser.

Hello api12,

Am I right assuming that you are referring to the grey lock with an orange triangle (and the information you get when you click on it)  ?

If so, would you please take a look at this article (you'll have to scroll down a bit).

The exclamation mark seems to be about loading an (posible not existing) image withthe URL of the home page.

• Loading mixed (insecure) display content “http://adultfamilyhomes.org/” on a secure page

The Web Console shows warnings on other pages as well about the presence of mixed content. So it is possible that the website changed recently to using a secure connection and hasn't checked all the links.

• https://adultfamilyhomes.org/home/booking-rooms/SLID1046

Maybe contact the website to look into this.

• https://developer.mozilla.org/en-US/docs/Web/Security/Mixed_content