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After I reinstalled my OS, I've tried to sign in firefox sync, but the account is unknown.

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I had to reinstall my Windows 7, and after I did that I installed Mozilla Firefox. I tried to sign in to my sync account but it says that the account is unknown. I had all my bookmarks and passwords saved on that account, and I did not save or export anything prior to reinstalling Windows 7 because I thought it were all saved on my account. I'm 100% sure I'm using the right E-mail adress.

I had to reinstall my Windows 7, and after I did that I installed Mozilla Firefox. I tried to sign in to my sync account but it says that the account is unknown. I had all my bookmarks and passwords saved on that account, and I did not save or export anything prior to reinstalling Windows 7 because I thought it were all saved on my account. I'm 100% sure I'm using the right E-mail adress.

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What Firefox version were you using before?

Firefox 29 and later have a new Sync version that use a Firefox account and only use the name and password and no longer use a separate Sync (recovery) key (the Sync key is automatically derived from the password of the Firefox account).

The new Sync version is completely different from the version that was previously used and you need to install a Firefox 29 or later version on all connected devices. You can enter the name and password of the Mozilla account on other devices that have a Firefox 29 or later version to add extra devices and you now longer can use a pairing key to pair a new device although this might be possible again in a future version of Sync if they decide to re-add this feature.

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I don't know which version I was using before, but I guess it wasn't outdated. Perhaps I've been using sync feature wrong and didn't really create firefox account. Thank you for your time.