First, I should mention that Sync takes time, and data may begin to appear gradually. However, if Firefox is idle and nothing is happening after 15 minutes, you may need to transfer some files.

Since the data you are looking for is a small set, perhaps you can drop in copies of three old files to work around this. The following steps are very verbose in case random strangers come by and want to follow along.

(A) On the about:profiles page, on the Root Directory row for the old profile, click the Open Folder button to launch that folder in Windows 10's File Explorer

Resize/position that source window on the left side of the screen (we are going to copy/paste left to right). Leaving that window open, switch back to Firefox.

(B) On the about:profiles page, on the Root Directory row for your live/working profile, click the Open Folder button to launch that folder in Windows 10's File Explorer

Resize/position that destination window on the right side of the screen. Leaving that window open, switch back to Firefox.

(C) Exit Firefox using the menu (menu button > Exit, or on the menu bar, File > Exit)

After allowing time for Firefox to complete its shutdown routine, we're going to rename the working files in the live profile in case you need them later, and/or in case your windows are switched.

(D) In the destination window on the right side:

• right-click the logins.json file, click Rename, then assign a name like loginsOLD.json and press Enter or click away to complete the edit
• right-click the key4.db file, click Rename, then assign a name like key4OLD.db and press Enter or click away to complete the edit

(E) Starting in the source window on the left side, transfer the saved logins files:

• (left side) right-click logins.json, then click Copy
• (right side) right-click a blank area of the file listing in the destination window on the right side and click Paste

• (left side) right-click key4.db, then click Copy
• (right side) right-click a blank area of the file listing in the destination window on the right side and click Paste

(F) Transfer bookmark backups:

In the source window on the left:

• Double-click the bookmarkbackups folder to open it -- Firefox should display numerous files with names similar to: bookmarks-2021-10-18_1045_gibberish==.jsonlz4
• Select all of the backup files using Ctrl+A.
• Right-click any file, then click Copy

In the destination window on the right:

• Double-click the bookmarkbackups folder to open it -- probably this is empty or just has a small file for today
• Right-click a blank area of the folder and click Paste -- Windows should drop in all the files you copied in the other window

(G) Start Firefox

Firefox should automatically detect the copied-in logins files.

To restore one of those bookmark backups, use the steps in this article: Restore bookmarks from backup or move them to another computer.

Success?

Note that the current release is Firefox 93.0, so with Firefox 91 you are a few versions behind.

You can find the full installer of the current Firefox release (93.0) in all languages and all operating systems here:

• https://www.mozilla.org/en-US/firefox/all/#product-desktop-release
• https://www.mozilla.org/en-US/firefox/93.0/releasenotes/