Product Version = NetBeans IDE 8.1 (Build 201510222201)
Operating System = Mac OS X version 10.11.1 running on x86_64
Java; VM; Vendor = 1.8.0_65
Runtime = Java HotSpot(TM) 64-Bit Server VM 25.65-b01

Reproducibility: Happens every time

STEPS:
*  Installed Explored from here NetBeans Module from certified module
http://efhnbm.sourceforge.net/
1) 
*  Select packages by right clicking
*  Select "Explore with Mac OS X"

ACTUAL:
  Can't find a good explorer /prompt for Mac OS X

EXPECTED:
  Using Mac's Finder and expore to the file directory of the package.

SOLUTION :

2) 
* Select Netbeans/ Preference / Miscellaneous

Remove below commands : (which is for windows)
rundll32 url.dll,FileProtocolHandler {0}
explorer /e,/select,{0}

Add in below commands : (which is for Mac's finder)
open {0}

Suggestion :
a. Revised the user interface to add in an option as mac. 
b. Add in this feature as module default
c. Add this plugin into default feature of Netbeans IDE.