Yeah, I did this one time and I was not happy.

Any data you have on the server will be erased when you reset your password. Your other devices will stop synchronizing unless you update them with the new password.

When you change your Firefox Account password, the existing data is deleted. (I've lost my Firefox Sync account information - What to do)

Do you have any backups of your disk from before the reinstall, or did you use any Windows feature like reset or refresh that may have stored your data in a new temporary folder here:

C:\Windows.old

Can you find such a folder on your system?

If so:

Before proceeding, please set Windows to show you hidden files and folders: https://support.microsoft.com/en-us/help/14201/windows-show-hidden-files

Then check here:

C:\Windows.old\Users\<user>\AppData\Roaming\Mozilla\Firefox\Profiles\

You might just have one profile folder, or you might have more than one. Anything there?

Set this and it will help the next time.

https://support.mozilla.org/en-US/kb/reset-your-firefox-account-password-recovery-keys