Keep is simple and use Sync. see screenshots https://support.mozilla.org/en-US/kb/how-do-i-set-sync-my-computer https://support.mozilla.org/en-US/kb/how-do-i-choose-what-information-sync-firefox

I am *not* willing to uploads sensitive browser data to the cloud.

Please advise on how to make the "Import from another browser" tool do what it says it does.

Have I encountered a bug?

Thanks

What Firefox version did you install (?distro) ? A Firefox Snap version might not detect a regular Firefox ESR version. If you use the snap version then try Firefox from the Mozilla server.

• https://www.mozilla.org/en-US/firefox/all/#product-desktop-release

You can copy certain files with Firefox closed to the current profile folder to transfer or recover personal data. Note that best is to avoid copying a full profile folder.

• bookmarks and history: places.sqlite
• favicons: favicons.sqlite
• bookmark backups: compressed .jsonlz4 JSON backups in the bookmarkbackups folder
• cookies.sqlite for the Cookies
• formhistory.sqlite for saved autocomplete Form Data
• logins.json (encrypted logins;32+) and key4.db (decryption key;58+) for Passwords saved in the Password Manager
  key3.db support ended in 73+; to use key3.db in 58-72, make sure to remove key4.db
• cert9.db (58+) for (intermediate) certificates stored in the Certificate Manager
• persdict.dat for words added to the spell checker dictionary
• permissions.sqlite for Permissions and possibly content-prefs.sqlite for other website specific data (Site Preferences)
• sessionstore.jsonlz4 for open tabs and pinned tabs (see also the sessionstore-backups folder)

107.0.1 is my new Firefox version. From Debian Sid. Not sure what a snap is.

I will try moving those files over this weekend. Thanks for the details.