In the event that the passwords information is lost, you should record all information in a separate text file somewhere else on your hard drive, or written down. You can easily copy and paste if you need to do so. If you are concerned about someone else looking at that file, you can compress it using a password.

I take it you are talking about sync?

Resetting the sync password will remove all data from the servers. This is a security feature. I've lost my Firefox Sync account information - What to do

That did not answer the question...at least in English

We have no way to get a missing/lost password.

However, I do not know my user name and password

Assuming you are talking about Firefox Sync.

Do you still have the old computer? If so, get your user name and password from the Firefox Password Manager on the old computer. And if you don't have the old computer any longer or it doesn't work, what about other devices connected to that Sync account?

Beyond that, I'm not sure how we can help you. The email address that you used when you signed up for Sync is your user name; if you can't remember that you are totally SOL.