You will need to install the latest java plugin, ie 1.8.x
The browsers won't let you run older versions of java anymore.
There are parches to apply for IE11 compatibility. You may be able to open forms with Firefox ESR 32-bit only.
R12: Recommended Browsers for Oracle E-Business Suite (Doc ID 389422.1)
Chrome requires the latest Java Web Start patches to be applied and you have to code sign your JAR files.
Using Java Web Start with Oracle E-Business Suite (Doc ID 2188898.1)
Deploying JRE (Native Plug-in) for Windows Clients in Oracle E-Business Suite Release 12 (Doc ID 393931.1)
Enhanced Jar Signing for Oracle E-Business Suite (Doc ID 1591073.1)
R12 E-Business Suite Java / JRE Upgrade Does Not Correctly Update The 3 Digit Version Of Java Installed In The Context File, Forms Applications, Or Java Console (Doc ID 2227147.1)