Your Mozila account syncs your passwords, bookmarks and history across multiple devices. If you notice suspicious activity on your Mozilla account (like someone signing in from an unknown device), there are steps you can take to prevent further access to your information.

First, change your Sync password from a synced computer

This first step will prevent devices with your old Mozilla account password from connecting to the Sync server and getting all of the new passwords that you will have to create in the next section.

1. Click the menu button to open the menu panel.
2. Click your Mozilla account (your email address or sign in).
3. Click Manage Account (or visit https://accounts.firefox.com).
4. On the Mozilla account page, scroll down to the Security section and click the Change button next to Password.
5. Follow the steps to enter your old and new passwords, then click Save to finish.

Second, change all of your website passwords from a synced computer

This part is more time consuming but important. If you don't change the passwords for things like your bank account, it would still be possible for someone else to log in to your account using the existing already synced password.

See Create secure passwords to keep your identity safe for an easy way to create better passwords.