Easiest would be to install Firefox 52 ESR on the new computer along with its profile and update this version until you reach the new version to allow migration code to update profile files to new schemes.

Firefox 32 and newer use logins.json instead of signons.sqlite to store the passwords. Firefox 58 and newer use key4.db (SQLite) for the key file and no longer use key3.db (DBM), but can use key3.db as a fallback when key4.db is missing. Support for key3.db ended with Firefox 73 and newer (i.e. Firefox 72.0.2 is the last version that supported key3.db) and thus 73+ versions can't be used to migrate logins.json and key3.db to key4.db.

Firefox versions prior to Firefox 58 can use SQLite databases by using a special environment variable (NSS 3.12;2011), so this isn't really something new. Only in Frefox 58 the SQLite format got enabled by default.

NSS_DEFAULT_DB_TYPE=dbm : key3.db - cert8.db - secmode.db
NSS_DEFAULT_DB_TYPE=sql : key4.db - cert9.db - pkcs11.txt

You can install Firefox 72 and create a new profile and put logins.json and key3.db files in this profile. You can use Sync to sync the logins to the current release.

I installed Firefox 72 copied logins.json and key3.db start Firefox 72 but no logins I could see but key4.db created on exit

Did you make sure that there is only logins.json and key3.db and not a key4.db file present to force Firefox to create a new key4.db as otherwise Firefox would use this existing key4.db instead ?

Yes I deleted key4.db before launch ff 72. But after launch no logins present.

You can give the conversion another try and set signon.debug = true on the about:config page and repeat setting only key3.db and logins.json in the profile folder. You can start Firefox and check the Browser Console (Ctrl+Shift+J) for login related messages. You may have to open the Password Manager. You can clear the messages beforehand and only enable Errors and Warnings, hidden items may have an item count appended. Do not forget to reset signon.debug to false after you are done testing.

• https://firefox-source-docs.mozilla.org/devtools-user/browser_console/

It worked. Thank you very much.