Can't connect to accounts.firefox.com
I cannot load https://accounts.firefox.com. I get the "Unable to connect" page. Opening a dev console doesn't show anything odd in logs. I tried following the steps on this page https://support.mozilla.org/en-US/kb/firefox-cant-load-websites-other-browsers-can to no avail. It doesn't work under safe mode either. Other browsers on this same machine load the site just fine. Anything else I can test?
There is security software like Avast, Kaspersky, BitDefender and ESET that intercept secure connection certificates and send their own.