If you get this Korsakow flash error in the browser:

Application.onDomainLoadError: SecurityError: Error #2148

This is the fix from Florian:

1.
Uninstall Flash:
https://helpx.adobe.com/flash-player/kb/uninstall-flash-player-mac-os.html

2.
Install the previous version of Flash.
Flash player version that works on Firefox OS X 10.12 – 22.0.0.209
Archive of Flash Player Versions:
https://helpx.adobe.com/flash-player/kb/archived-flash-player-versions.html