In the Menu bar at the top of the screen, click Firefox and then select Preferences or Settings, depending on your macOS version.Click the menu button and select Settings.
Go to the Sync panel and click the arrow next to Manage Account to expand the menu.
Click Change Password. The Change Your Password window will pop up.
Enter your new password and click Change Password.
Close the Settings page. Any changes you've made will automatically be saved.
and select .