Yes, it was The Main toolbar (+ when device is connected). These two are selected for default placement of the icon when installing some Interface Action Plugin. Probably most users just say Yes and that's it. On two fresh Calibre (and then fresh plugin installation) OSX installations first pass didn't get to the usual pop-up (asking about placement of the icon).
That happens sometimes and then it is recommended, after restart, to find the icon in Calibre > Preferences > Toolbar and select in which menu bar one will find the plugin icon.
The reason why that didn't happen is that OSX didn't properly closed Calibre. When it was done through terminal saying: `calibre-debug -s` and started again the icon appeared in menu bars and one could select it for menu bar they want.
I know that just closing window doesn't properly shut down application on OSX. It should be quit. Still, people told me they quit it, not just closed it. Strange. I don't have OSX so my troubleshooting relies on OSX people claiming what they did. I write this feedback here because it will maybe happen again to other people and `calibre-debug -s` in terminal will help.
When I get a chance to debug this on some Apple machine i'll do my best to find the better solution... I promise
