Resetting the sync password, or changing its e-mail or password, will remove all data from the servers. The username and password are used to create the encryption.

This is a security feature. https://support.mozilla.org/en-US/kb/ive-lost-my-firefox-sync-account-information

• I've lost my Firefox Sync account information - What to do
• I’ve forgotten, or don't have access to, my Firefox Account email address

Note: Only the data on the servers is cleared. The profile data is not changed or removed.

When I want to delete my Firefox account I am told that I am likely to lose all my settings including the bookmarks on my computer. How can I avoid this ? I want to keep my bookmarks on the computer, not on the servers.

Note: Only the data on the servers is cleared. The profile data is not changed or removed.

Do you have other devices connected to this Sync account ?

Note that Sync isn't meant to be used as a backup, but is merely meant to Sync data between connected devices, so if you only have this device then there is no need to use Sync.

I have used Sync once to sync two devices and I want to delete the data in the account now.

In the meantime all my bookmarks from my laptop have disappeared (without deleting my Firefox account). How can I restore them ?

What about the rest of your profile? Settings, bookmarks, history, passwords . . . .

Look on your desktop. Do you see a folder called; Old Firefox? Look inside. Look for the folder with the latest creation date.

https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

https://support.mozilla.org/en-US/kb/how-run-firefox-when-profile-missing-inaccessible