Unable to access OEM 11g grid control after upgrading to Firefox ver 39.0 Previously, I have encountered the similar issue after upgrading Firefox to version 37.0.1. 

Here's the link of the question posted: Unable to access OEM 11g after upgrading to Firefox ver 37.0.1

I applied the suggested workaround Set Firefox's about:config setting security.tls.version.fallback-limit to '0'. It worked for Firefox version 37.0.1 however, yesterday my firefox was updated automatically to verson 39.0 (I have since disabled the auto update). Everything broken again. 

Working around no longer fix. Not sure what Firefox has done with the new release.
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.