How to exit Firefox kiosk mode?
Solution 1:
After all I found that I can start Firefox in safe mode, which starts it with alle extensions switched off. This Mozilla knoledge base article describes how to do that for your os.
In safe mode I could see that the kiosk mode was done with the R-Kiosk add-on.
Solution 2:
If you press F11 firefox will exit fullscreen/kiosk mode
Solution 3:
The question asks about exiting kiosk mode for the purpose of identifying the settings to see how it was set up so it can be replicated. This add-on will accomplish the kiosk mode for you: mKiosk: Public Firefox Kiosk Multimedia
Addon description:
Public Firefox Kiosk Mode with optional Tabs Guides for Access Point. Complete solution. Block downloads/addon, bookmarks, reset kiosk inactivity, retry on errors, restricted interface, show favorites as buttons and more.