Unable to access OEM 11g grid control after upgrading to Firefox ver 39.0
Well, I have finally figured it out. I clicked on 


Opened Help Menu (?)
Troubleshooting Information
Refresh Firefox


This would reset the default Firefox configuration. You will lose all your add-ons. Beware!

Next, enter following in browser URL: 

about:config


Change the following settings
security.tls.version.fallback-limit=1 

Restart firefox.

Viola! OEM loads flawlessly.