There's nothing Firefox users can help here if you lost email access and lost the passcode nothing can be done. They have email reset but if you don't have access to the Primary email registered then that lost as well.

Hi team, I have misplaced my device and forgotten the 10 recovery digits for my Firefox account. The account had an add-on with over 1,000 downloads. Is there any way to recover my previous account using the email associated with it? I am curious as to why Firefox doesn't offer email-based account recovery.

If you were using this with addons.mozilla.org then there is a small possibility you could get help at https://discourse.mozilla.org/c/add-ons/35