If you lost all of your own bookmarks, you may have created a new profile and are using that.

To get to your profile use about:support then click on "Open Containing Folder" note the filename -- it contains your profile name plus hash characters. Next go up one directory, and see if you have other profiles. Within each profile check the dates within places.sqlite, and the JSON files within the bookmarkbackups directories. Would also suggest taking Firefox down and backup up everything from the "profile" directory down(copy do not move your files) -- it should all fit an a typical thumb drive. When finished -- Safely Remove the external device so that all files are written to it before removal.

See

• Lost bookmarks - MozillaZine Knowledge Base
  http://kb.mozillazine.org/Lost_bookmarks

You may find solutions here but less likely than in the above:

• after booting my system I can't find my bookmarks and I can't restore from a cd | Firefox Support Forum | Firefox Help
  https://support.mozilla.com/en-US/questions/839705
• Can you copy bookmarks from old Windows installation (copy of AppData folders) into a clean Windows7 install | Firefox Support Forum | Firefox Help
  https://support.mozilla.com/no/questions/757470
• Had to wipe disks and reinstall everything. Lost all bookmark and speeddial data. How do I get back to where I was? | Firefox Support Forum | Firefox Help
  https://support.mozilla.com/gl/questions/768299
• How do I find and restore my old profile using Mozilla 3.6.13 after uninstalling Mozilla 4.0 Beta 9? | Firefox Support Forum | Firefox Help
  https://support.mozilla.com/sr-CYRL/questions/787225
• How do I recover my list of bookmarks following hard disk reformatting and re-installation? Data files were saved and copied back. | Firefox Support Forum | Firefox Help
  https://support.mozilla.com/en-US/questions/774468
• Lost bookmarks, solutions listed don't work. | Firefox Support Forum | Firefox Help
  https://support.mozilla.com/en-US/questions/840903
• My bookmarks are gone and I want them back -- DO NOT TELL ME TO SEE YOUR LOST BOOKMARKS SECTION, I ALREADY HAVE AND IT IS NOT RELEVANT. | Firefox Support Forum | Firefox Help
  https://support.mozilla.com/ilo/questions/688895

See also:

• http://kb.mozillazine.org/Bookmarks_history_and_toolbar_buttons_not_working_-_Firefox

thank you dmcritchie and cor-el.

After posting my question I searched around and found how to restore my bookmarks:

Select: > bookmarks in menu bar > all bookmarks > restore

a menu appeared to show a selection of previous dates to restore. I selected the day before my installing new Firefox version and voila! All my bookmarks are back!

CLICK ON BOOKMARKS AND AT BOOTOM OF DROPDOWN CLICK ON UNSORTED BOOKMARKS...IN LIBRARY CLICK ON IMPORT & BACK UP... MOVE MOUSE OVER RESTORE AND HOPEFULLY YOU SHOULD SEE LIST OF DATES.......CLICK ON ONE THAT PRIOR TO THE DASTE YOU DID UP GRADE....IT IF WORKS FOR YOU THEN YOU SHOULD GET BACK BOOKMARKS THAT YOU HAD ON THAT DAY..........

GOOD LUCK SCEEBUCK

I tried to restore from backup dates. None of the dates worked!! The error message was "unable to process backup." What do I do?

Did you try to deleted all the places files in the Firefox Profile Folder to see if that makes restoring work?<

If that still doesn't work then the file may be corrupted.
You can also try one of the older backups in the bookmarkbackups folder if you haven't done that yet.

• http://kb.mozillazine.org/Unable_to_process_the_backup_file_-_Firefox