Posting my comment from bugzilla:

> I think I would suggest to rephrase as follows:

> Array of group constants that menu may be placed in. Note that menu item will appear only under one, most appropriate parent from the given options. Add-on's provides is given from left to right. This enables add-ons to handle different platforms in order of their preference (note not all groups will be available
on all platforms).

> I don't like that this property is string or number or array of them. I think it
should always be an array and instead of string or numbers we should expose constants with readable names representing different parent groups. This would
also align with identical approach in places API. This is also going to allow us
to start with just a few well thought out groups and later we may add more.