If you have a lot of bookmarks then the initial sync can take quite some time to finish, so it sounds that you didn't complete this initial sync.
However you should still have the profile folder from your previously used Firefox version and if both versions (regular and ESR) are on the same computer then you can merely copy related files form one profile folder to another profile folder.
If they are on different devices then you need to use a USB stick to transfer the files.

You can copy files like these with Firefox closed to the current profile folder to recover specific data.

• https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

• 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 (passwords) and key4.db (58+) or key3.db (57 and older) (decryption key) for Passwords saved in the Password Manager
  if you only have key3.db then make sure to remove an existing key4.db
• cert9.db (58+) or cert8.db (57 and older) for (intermediate) certificates stored in the Certificate Manager
  if you only have cert8.db then make sure to remove an existing cert9.db
• persdict.dat for words you added to the spelling 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)

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

• Help -> 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

... I DID check bookmarks, etc to be synced to the new version but they are all gone!!! ... es, i did have to set a new identity as it asked me to during the download process for the new version. ...

If you reset the Firefox Account password when trying to login to connect to Sync, your Firefox data (including bookmarks) would have been cleared from the Sync server. All Sync data is encrypted thru the original account password, another password won't work; so the data is deleted to allow the account to continue to be used.

As far as "new identity" goes; that might be the Profile which is what cor-el addressed.