cdtaylor nats has it (post #9)
This is the response I received from a helpful MS Outlook consultant,Jenely C. It fixed this issue for me.
The issue SEC error upon opening using Firefox browser has now been tagged as an emerging issue. Our developers as well as our higher level of technicians are now aware of this issue and in collaboration in providing the best possible resolution.
For the meantime you can try to follow these temporary fix in order to access your account in Firefox browser.
Here are the steps:
-open Firefox
-on the address bar, type 'about:config' (confirm the info message in case it shows up)
-search for the preference named 'security.ssl.enable_ocsp_stapling'
-double-click it and change the value from 'true' to 'false'
-re-launch firefox