Sorry to hear about that. Hope your bookmarks and history can provide some ways to look back on the sites you visited. It's curious how an extension released two weeks ago (3/6/2018) can facilitate a full month of hardcore research work already. But anyway, I'm sorry you lost your work and hope you can recover your links.

Anyway, I have tried to replicate the problem. I had a fresh install of Firefox, installed Session Boss 1.0, saved lots of tabs and windows and sessions, and upgraded to 1.1. The old sessions were still there. Then upgraded to 1.2. The old sessions were still there. I've tried these on both Firefox 57 and the latest 59. Same result.

Session Boss stores data in Firefox's profile folder, see the "Browser extension storage and offline backup" section on where the extension data file is. See if the data file is still there. The extension data file can be backed up offline.

Since the extension data file is tied to the profile, using a different Firefox profile will not see the original saved session. See if you are using a different profile when upgrading.

Refresh Firefox would also wipe out all extension data.

Reply2:

- Can you use Undo to get back to a previous snapshot of the user sessions? There are left and right arrows at the top of the extension popup UI, in the middle of the top bar. The left arrow is for Undo.

- Does the Auto Backup Sessions have one of your older sessions? Auto backup session is saved in addition to the older backup sessions. Even if the current browser has empty pages and is backed up, the older backed up sessions still have the data.

Reply3:

It's quite concerning regarding FF support's reply on the data file managed by Firefox being corrupted. As extension developers, we use the storage API Firefox provided to store data. We don't know nor should we care whether Firefox uses one file, multiple files, or a database to implement the API to store data. We trust Firefox would do a good job to provide a reliable implementation to the API. In fact, none of the documentation on the API [1] mentions any of the implementation detail. Nor does it have any warning about its reliability. I mean if it's unreliable, they should put a warning there. It's just a big waste of time.

For now, please back up the storage.json file periodically, till I figure out what's the next step. Only started to do development for Firefox and it's not very encouraging...

[1] https://developer.mozilla.org/en-US/Add-ons/WebExtensions/API/storage/local

Reply4 to QUESTION:

- I have no control over saving the data to one file or to separate files. The Firefox implementation makes that decision underneath. In fact I've already designed data versioning into the extension - any user changes are stored as a new snapshot version while the old versions are not touched, to avoid accidental overwrite. That's why Undo/Redo functionality can work to roll back changes. But all that precaution are meaningless if Firefox storing everything in one file underneath.

Anyway, I need to figure out the next steps.