On Windows and Linux you can get contextual help in JMC by pressing F1 at any time. On Mac, this does not work.
Normally on Windows, F1 is used to display help, but on Mac it is ⌘?. If you check the keybindings in Prefs on Windows (or with Ctrl+Shift+L – keep pressed to open Prefs dialog!), there doesn't seem to be a keybinding for context help, but it still works.
I suggest we use Fn F1 for contextual help on Mac.