I've forgotten my Firefox Account password — how do I reset it?

1. Click the Firefox Account icon in the toolbar.
2. Click Turn on Sync.
3. On the Sign in page, click Forgot password? ...
4. Follow the instructions in your reset email to change your password.

https://support.mozilla.org/en-US/kb/ive-lost-my-firefox-sync-account-information

The Firefox account name is the email address that you used when registering that Firefox Account for Sync and other Mozilla features.

Password is important, without the exact password any data sitting on the Sync server is useless. No way to decrypt that data to get it back into Firefox.