Hi @Seeker220 and welcome to the community 
I don’t think that’s a problem with Firefox Developer Edition. It seems there is something between you an Google that acts as a “Man in the Middle”. Most likely an Anti-Virus (doing TLS inspection) or a captive portal of a public WiFi. Someone doing evil things could also be possible.
Could you press the “Advanced…” button on this screen and show us the message that appears? It would also be helpful to then click on “Show certificate” inside there and show us which certificate is presented.
Thank you very much!
Michael
In recent months, many users’ connections to Google properties are getting proxied by an unknown program or entity (“man in the middle”). Try setting “No proxy” and test again.