Hi, I'm a Redux maintainer.
We recently released React-Redux v6 [0]. The major change for this release was how React-Redux internally makes the Redux store state accessible to nested components, by switching from React's old (and broken) context API to using the new context API. I wrote a blog post about the technical details of the change and why we did it [1].
A number of libraries in the ecosystem were accessing the Redux store directly out of legacy context, which was not part of the React-Redux public API. Because of this, those libraries broke when used with v6 (as described in our release notes).
Note that this was not an issue with React or Redux themselves. This was caused by other libraries in the ecosystem relying on non-public implementation details, which are always at risk of breaking no matter what the library or language is.
As you noted, react-redux-firebase is working on updating itself to work correctly with the latest version of React-Redux. (We've also added some docs to React-Redux that describe how libraries can safely access the store directly [2], albeit with the caveat that this is still not directly part of the public API.) You can also stay on React-Redux v5 and the existing version of react-redux-firebase if you'd like. There's nothing specifically wrong with those versions, and they still work together.
Let me know if you've got any questions on this.
[0] https://github.com/reduxjs/react-redux/releases/tag/v6.0.0
[1] https://blog.isquaredsoftware.com/2018/11/react-redux-histor...
[2] https://react-redux.js.org/using-react-redux/accessing-store