Firefox is a browser not your email service. You need to check with their support about your email issues.

Thanks for the response. I first checked with my email service-Infinity/Comcast. The support told me to try accessing my email through another browser. I tried. It worked. I was able to see the incoming email addresses on another browser. But I am a Firefox fan. I will go back to Infinity/Comcast again. But, in the mean time, any other ideas?

Try troubleshooting to verify it's not something else causing Firefox to go bad.

https://support.mozilla.org/en-US/kb/troubleshoot-and-diagnose-firefox-problems