You can ask questions here or on the Firefox support page:
Contributors and moderators are there to help you. If you want to know whether someone is a moderator, there will be the word moderator next to their username.
Back to your problem, you simply change your password, using at least 15 a mix of alphanumeric and special characters, both uppercase & lowercase. Make sure that your email service says that your password is strong enough.
You can also enable two-step authentication which is proven to be very useful. Also check your email service settings. On Gmail, I know you can log out or report the computer/user who has logged in to your account.
There is also an official Mozialla article about what to do if you find suspicious activity on your Firefox account:
Hope I helped!