Hi

Yes, making sure that both have the same up to date version of Firefox is a good idea. This support article should help:

https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

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.

You can use the button on the "Help -> More Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page (Root directory).

• Help -> More Troubleshooting Information -> Profile Folder/Directory:
  Windows: Open Folder; Linux: Open Directory; Mac: Show in Finder
• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

• 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)

I copied the ones you listed except for this that I didn't understand at all:

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

Started up Firefox and voila! got my horde of tabs back and all bookmarks, apparently all my history, so I'm assuming everything else worked too -- yay!

Except I got a message:

Looking for your saved logins? Turn on sync or import them.

If you saved your logins to Firefox on a different device, here’s how to get them here:

   Create or sign in to your Firefox account on the device where your logins are saved.
   Go to Settings > Sync > Turn on syncing… Select the Logins and passwords checkbox.
   Visit passwords support for more help.

If your logins are saved in another browser, you can import them into Firefox

- - - -

Since I copied logins.json over, I presume the message means I need to follow through with whatever the rest of that means. I see a key4.db but hesitate to copy it until I know what "32+", "58+", "73+" mean.

I also see a bunch of files names "pres-1", etc. Are those what store my choices for what toolbars, etc. are displayed, and themes?

There are also six files in the "extensions" folder, and I'd like to recover those but without disturbing the ones I've already set up on the new machine.

But wow, this much already is a huge relief! I was really discouraged after following directions from a half dozen different sites and nothing at all worked!

Now if moving all my programs were as easy....

Hi Yes, making sure that both have the same up to date version of Firefox is a good idea. This support article should help: https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

Between this and cor-el's note about not copying the whole thing, I'm 90% there!

For the logins you need to copy logins.json and key4.db to transfer the passwords.

For anyone having trouble moving bookmarks to a new environment. Win 10 to Win 11 on a new machine. A method that worked for me is outlined here:

In Firefox’s opening page right click on the “Bookmark Toolbar”. This will expose a drop down menu, select and click on “Manage Bookmarks”. A “library” window will appear and on that you will find, in the left column, “Bookmarks Toolbar” left click on that and a list will appear to the right, with all the Bookmarks and Folders displayed. Choose each one separately, in the order you want them to display on your toolbar, starting on the Left and working to the right. Only one Bookmark or Folder will be handled at a time. Right click on the item you want to copy to the “Toolbar”. On the drop down menu choose “Copy”. Then go to your “toolbar” and right click then choose “Paste”. The Folders are already loaded with there respective bookmarks. It worked for me, good luck.