I use the password manager in Firefox for routine business like TFF, where nothing substantial is at stake. (Sorry.
) Passwords for financial or other private, secure or high-stakes stuff I never keep in Firefox or anywhere else in or on near the computers. I do try to keep an updated hard copy of all passwords stashed in a secure location. Every now and then my aging mind draws a complete blank on something.
A tip for the new, much longer passwords that some sites will require or accept: Find a long sentence, some phrase that has some meaning to you so that you won't forget it and use the first letter of each word, along with some related number. It has to be something that is easy to remember exactly the same way time after time.