I recently performed a new fresh install of the Oracle R12 E-Business Suite and all went smooth sailing until I opened web browser to launch Concurrent Manager administration screen in which R12 complained that it cannot find the J2SE plugin which is required for most administration screens on the client desktop. Since I am using Firefox for Linux, I tried the initial workarounds mentioned in MyOracleSupport (Metalink) note 414151.1
403 Forbidden Error When Download J2SE Plugin From Firefox In R12 to resolve the problem with Firefox and my R12 installation. Only problem is that since I am running client on a Linux machine, it did not open the oaj2se.exe file successfully.
So, turned to another Metalink Note 389422.1 Recommended Browsers for Oracle E-Business Suite Release 12 to see what browsers will work and allow me to install the plugin for J2SE with E-Business Suite for Release 12.
However, I wanted to use Mozilla Firefox as I prefer open source solutions for Linux.
So what to do? Since the required plugin is a windows file, you need to download the WINE package from http://www.winehq.org for Linux. Then you can install the plugin oaj2se.exe to fix the browser issues with R12 EBS. Even better, if you must use Microsoft Windows products, WINE allows you to do so with Linux!
Hope this helps.