While the rapid release trains provide a very good userbase for testing a feature, it's only at the release time that the "real world" feedback allows to prioritize improvements.
Unfortunately, at that time, there's the concrete risk of a disconnection:
- the user sends valuable feedback
- the development team is already busy on something else
Thanks to the open and transparent nature of the Mozilla project, the feedback is never lost, very often it naturally converts to bugs and discussions. On the other side this disconnection may cause a delay before actionable items are created.