I recently reinstalled Ubuntu. I opened Firefox preferences and tried to add my sync account.
I selected the option saying I didn't have my device with me, and proceeded. Next I entered my details and saw that something called a 'recovery key' was needed. I didn't remember seeing this before (and I've been using sync since it was called weave), so I clicked "Don't remember" and then "Generate new key".
It said it was succesful and that it would start syncing. But none of my data came through. I started getting worried. I searched the Internet and found this http://support.mozilla.org/en-US/kb/Replace%20your%20Sync%20information.
So it looks like all my years of data online has been removed without warning me. Sure, I should have backed up the data (and in fact I do have an older backup), but this still shouldn't happen without warning me. It's a big shock.
Has this happened to anyone else? Is there anything I can do about this?
Unfortunately there is nothing you can do about this. The key is what is needed to read your otherwise encrypted data, and there is no way around it. Even the Mozilla Foundation, that maintains the firefox sync servers, can't access your data without said key.
Such a mechanism is incredibly useful, as it guarantees you that nobody other than you will be able to look at your data. The downside is that, if you fail to keep the key, you lose all your data without any possibility of recovering it.
I would suggest that you write down your new key in a safe location, in case such a thing happens again. Keeping good backups is also essential.