I followed these steps on my fresh (Virtual) Mac OS 10.11:
1) Open up Safari and go to Oracle JDK download page:
And download Java SE Development Kit 8u101 for Mac OS X (jdk-8u101-macosx-x64.dmg)
2) Click downloaded file and Install Oracle JDK 8
3) Open up Safari again and go to FFDec download page:
And download Mac OS X Application (zipped) - ffdec_9.0.0_macosx.zip
4) Downloaded file is shown in Downloaded section, but it cannot be run directly by
clicking, since it is from unidentified developer (We do not want to pay Apple to be the
one - we are free project).
It displays message about unidentified developer with no option to run it anyway.
5) Click "Open in Finder" in the downloads menu
6) In finder, right click FFDec application (actually the downloaded zip file, but it has
FFDec icon since there is app insided) and popup menu appears.
7) In the popup menu, click "Open" item.
8) Another message about unidentified developer appeared, but this time, a button with
label "Open" is also present in the dialog.
9) Press the "Open" button in the unidentified developer dialog
10) FFDec launched correctly and its main blue window is displayed and looks like fully
11) From now on, direct clicking on application icon (actually the zip file) works too.
There's no longer dialog about unidentified developer.
This way it works for me.
Which other steps do you do to launch the application?