I haven't seen a detailed breakdown of the freedom problems with Firefox OS, but it looks to be more or less the same as Android in the cupcake era - really basic core applications and a phone that works, but not much third party stuff. You have to rely on mobile web sites. The biggest difference is that rather than have dalvik-based applications, they are written in javascript. All the core apps are on your device locally, and you can write code that is also stored locally too.
Then it promotes the whole "search" part. That seems to be links to websites mixed in with applications, which does seem confusing and doesn't sit well with having data independence. But that's just the same as using web sites on Android.
On the positive side, I'd trust Mozilla to maintain their first-party code as free software. The core phone apps are not likely to go proprietary, as seems to be happening on Android.
The killer cutoff is if it's possible to write server apps for the platform in question. For iOS you can while the app is in the foreground, for Android you can all the time, for Firefox or Chrome OS . . . nope, they are explicitly designed to be clients to something else.
That may seem ridiculous, but the hooks are not there in Web APIs to do peer to peer communication for example, let alone peer to peer based on discovery of nearby devices. Chrome OS even lacks zero conf network support. Aside from Mozilla (who seem overly attached to the support of carriers) the people pushing the advancement of the web platform have zero interest in altering this direction, and in fact would prefer we go further in it.
I would be far keener on FF OS or Chrome OS if they supported sandboxed node.js on the clients, and worked on extending the API from node.js, not the web browser model.
Then it promotes the whole "search" part. That seems to be links to websites mixed in with applications, which does seem confusing and doesn't sit well with having data independence. But that's just the same as using web sites on Android.
On the positive side, I'd trust Mozilla to maintain their first-party code as free software. The core phone apps are not likely to go proprietary, as seems to be happening on Android.