Как перенести в Firefox на свежеразвёрнутом компьютере?

"Гмм... "...сходу не знаю, как перенести сохраненные пароли в чистый профиль". Это есть на странице Mozilla о работе с профилями. В каталоге Firefox'a найти и сохранить файлы key3.db и signons.sqlite и заменить ими соответствующие в новой установке или профиле. Закладки -- places.sqlite. Список аддонов -- из меню -- Справка -- Информация для решеня проблем или однострочником:
jshon -e addons -a -e defaultLocale -e name -u < ~/.mozilla/firefox/*.[dD]efault/extensions.json
(если установлен пакет jshon)."

Взято здесь

UPD c mozilla.org

Passwords

Your passwords are stored in two different files, both of which are required:

• key3.db - This file stores your key database for your passwords. To transfer saved passwords, you must copy this file along with the following file.
• logins.json - Saved passwords.

Site-specific preferences

• permissions.sqlite

This file stores many of your Firefox permissions that are decided on a per-site basis. For example, it stores which sites are allowed to, or blocked from setting cookies, installing extensions, showing images, displaying popups, etc.

Search engines

Personal dictionary

• persdict.dat

This file stores any custom words you have added to Firefox's dictionary. If you have never added a custom word to the Firefox dictionary, then you will not have this file. For more information see How do I use the Firefox spell checker?.

Autocomplete history

• formhistory.sqlite

This file remembers what you have searched for in the Firefox search bar and what information you have entered into forms on websites. For more information see Control whether Firefox automatically fills in forms.

Cookies

• cookies.sqlite

Cookies are used by websites for a variety of reasons, some of which include keeping you logged in to a website you have previously logged in to, remembering any preferences a website has allowed you to set, authenticating you as a person who has visited a specific website before, etc.

Security certificate settings

• cert8.db

This file stores all your security certificate settings and any SSL certificates you have imported into Firefox.

File types and download actions

• mimeTypes.rdf

This file stores your preferences with respect to what Firefox does when it comes across known file types, such as whether you want to save a file or open it with a specific application. For more information see Change what Firefox does when you click on or download a file.

Vivaldi

На новом месте разворачиваем Vivaldi и запускаем его для создания первоначального профиля в /home/%user%/.config/vivaldi. Vivaldi останавливаем. Затем замещаем файлы нового профиля файлами старого.