Firefox's recent stable release channel version 52.0 update ends NPAPI plugin support for Java, Microsoft Silverlight and Adobe Acrobat (Adobe Flash is not affected, however, no support end date for this plugin has been communicated). The impact for Oracle E-Business Suite (EBS) customers using Firefox is that even though they have the latest version of Java installed on their system, Firefox will not recognize and load the associated Java plugin.
A morsel of good news for Firefox-EBS users is that a temporary workaround does exist for those who still want to utilize the Firefox browser.
BTW and regardless of version, for Windows, EBS only supports the 32-bit version of Firefox. So, when you click the link above, find your language and click the link in the Windows column (not the Windows 64-bit) column.
The only drawback to running this version (as opposed to Version 51), is the annoying message below User Name and again below Password. Once you are logged in, the message does not repeat.
Alternatively, you can download and reinstall Version 51 from Firefox version 51. Click the top link.
Steven Chan's Oracle E-Business Suite Technology blog of March 13, 2017, explains this further.
When in doubt about any browser issue, version or setting, the definitive source is My Oracle Support note 389422.1 – Recommended Browsers for Oracle E-Business Suite Release 12 and note 393931.1 – Deploying Sun JRE (Native Plug-in) with Oracle E-Business Suite Release 12.