Insecure login due to firefox?

I am a newbie and this morning when i went to my login info was already filled in including my master password. This is obviously not secure as anyone could get into my bitwarden.
Is it possible that firefox is saving all of my passwords to ease logins to my sites? Should that feature somehow be stopped?

It sounds like you have your browser configured to remember your passwords. You can turn it off in your FF settings (disable saved logins).