Hi alinehw, are you able to update your passwords using a trusted system, meaning, a computer or iOS device that isn't compromised? If so, that would be the first step to make sure anyone who knows your earlier password is no longer able to access your accounts.

After that, you should work with the service providers (Yahoo, AT&T, and Instagram/Facebook) on whatever is needed to clean up the mess.

Firefox itself is a web browser and Mozilla has no access to your emails.