FULL PRODUCT VERSION :
java version "1.8.0_91"
Java(TM) SE Runtime Environment (build 1.8.0_91-b14)
Java HotSpot(TM) Client VM (build 25.91-b14, mixed mode, sharing)

ADDITIONAL OS VERSION INFORMATION :
windows 7 64 bit SOE release v 1.4

EXTRA RELEVANT SYSTEM CONFIGURATION :
The same applet is initialized and desired output is achieved in internet explorer version 11.0.9600.18230.

A DESCRIPTION OF THE PROBLEM :
The initializing the applet on firefox version 46 fails and gives following exception.The same applet is initializing fine in internet explorer version 11.0.9600.18230.

Java Plug-in 11.91.2.14
Using JRE version 1.8.0_91-b14 Java HotSpot(TM) Client VM
User home directory = C:\Users\xyz
----------------------------------------------------
c: clear console window
f: finalize objects on finalization queue
g: garbage collect
h: display this help message
l: dump classloader list
m: print memory usage
o: trigger logging
q: hide console
r: reload policy configuration
s: dump system and deployment properties
t: dump thread list
v: dump thread stack
x: clear classloader cache
0-5: set trace level to <n>


Exception in thread "AWT-EventQueue-2" java.lang.IllegalStateException: Applet's parent container not set up
at sun.plugin2.applet.Plugin2Manager.start(Unknown Source)
at sun.plugin2.main.client.PluginMain$StartAppletRunner.run(Unknown Source)
at java.awt.event.InvocationEvent.dispatch(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$500(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)


REGRESSION. Last worked in version 8u77

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1) Write a basic java applet
2) write code to initialize the applet
2) invoke the applet from firefox version 46 which will include initializing

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The applet should be initialized and desired output of applet is achieved.
ACTUAL -
The initializing the applet on firefox version 46 fails and gives following exception.The same applet is initializing fine in internet explorer version 11.0.9600.18230.

Java Plug-in 11.91.2.14
Using JRE version 1.8.0_91-b14 Java HotSpot(TM) Client VM
User home directory = C:\Users\xyz
----------------------------------------------------
c: clear console window
f: finalize objects on finalization queue
g: garbage collect
h: display this help message
l: dump classloader list
m: print memory usage
o: trigger logging
q: hide console
r: reload policy configuration
s: dump system and deployment properties
t: dump thread list
v: dump thread stack
x: clear classloader cache
0-5: set trace level to <n>


Exception in thread "AWT-EventQueue-2" java.lang.IllegalStateException: Applet's parent container not set up
at sun.plugin2.applet.Plugin2Manager.start(Unknown Source)
at sun.plugin2.main.client.PluginMain$StartAppletRunner.run(Unknown Source)
at java.awt.event.InvocationEvent.dispatch(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$500(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)


ERROR MESSAGES/STACK TRACES THAT OCCUR :
Java Plug-in 11.91.2.14
Using JRE version 1.8.0_91-b14 Java HotSpot(TM) Client VM
User home directory = C:\Users\xyz
----------------------------------------------------
c: clear console window
f: finalize objects on finalization queue
g: garbage collect
h: display this help message
l: dump classloader list
m: print memory usage
o: trigger logging
q: hide console
r: reload policy configuration
s: dump system and deployment properties
t: dump thread list
v: dump thread stack
x: clear classloader cache
0-5: set trace level to <n>


Exception in thread "AWT-EventQueue-2" java.lang.IllegalStateException: Applet's parent container not set up
at sun.plugin2.applet.Plugin2Manager.start(Unknown Source)
at sun.plugin2.main.client.PluginMain$StartAppletRunner.run(Unknown Source)
at java.awt.event.InvocationEvent.dispatch(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$500(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)


REPRODUCIBILITY :
This bug can be reproduced always.