I want to sync my desktop and mobile login lists. I have Firefox 95.2.0 (2012-12-16) on my phone. And I have 95.0.2 on my desktop. Everything on mobile marked to synchronize. I've even manually clicked "sync"... Phone says everything was uploaded. But nothing is in the list on the desktop. When I tries to add a "new device" in preferences on desktop, I expect it to give me QR code. But it gives me instantly "Synchronization failed" instead. I'm tired to open list on phone and then type everything in on desktop. How can I fix the issue?
You can install the About Sync extension in Firefox 72 and newer on desktop to check what data is stored on the Sync server via the about:sync page provided by this extension.
Close and restart Firefox to access the about:sync page added by this extension (see the about:about page for possible about pages).
You can open about:sync-log via the location bar to see if recent Sync logs are available. You can upload the file to a website like Pastebin if you can't post the content of the file in a reply.