I wish they fixed the long standing, annoying sync bug that makes Firefox download 7000+ containers every once in a while. Some of us hosed our sync accounts in one way or another (through the container duplication bug in m-a-c itself [1] or the temporary containers extension [2]) and it's impossible to recover - once you reach the storage quota on the sync server, the sync server refuses all write operations and delete call apparently counts as a write.
it is possible to recover! you just have to reset your account password, which blows away all server data, starting the quota over. but this is ok because you should still have a local copy, and when you log in with the new password you can upload that.
Thanks! I have been following the issues and also spent quite some time trying to fix/work around this on the client side, but it never occurred to me that simply reseting the password deletes everything server-side. I'll try it out.
[1] https://github.com/mozilla/multi-account-containers/issues/1...
[2] https://github.com/stoically/temporary-containers/issues/371