We are running SPE 7.5.1 on Oracle Linux 6.6 . We have a requirement that we have to use the Security Notice feature to put up a splash page before allowing a login to the GUI interface. If any text is put into the Security Notice field (either via the GUI, or by editing the SYMCScan/bin/configuration.xml file) then Firefox (tested with v34 - v38) will not start the Java plugin. Internet Explorer still works and will show the Security Notice splash page. To fix this, you have to remove all of the text (disabling the flag does not fix it, the text must be removed), and then Firefox will work again to access the GUI. Since we have some workstations that are Linux based (so no access to Internet Explorer), we have to have Firefox working.
This is easily reproducible for us on multiple systems running SPE.