My internet provider retired domain name "@q.com" and changed my account to "@myctl.net". How can I update Firefox?

This is interesting. Do you still receive emails for @q.com ? Normally, there should be a transition period that you can receive emails for both @q.com and @myctl.net. If yes, you can change your primary email address: https://support.mozilla.org/en-US/kb/change-primary-email-address-firefox-accounts If not, I think you need create a new Mozilla account using your new email address.