How did you lose the bookmarks? Did you copy the profile from the old systeem? How?

No, when i bought the new computer the engineer transferred everything on my new one which has windows 11. I don't`know what he has done or how,but i left it with him because it took few hours to transfer everything. This was done by the technical at Currys PCworld

Has anyone got a solution for my problem, please?

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Go to that message, and use the Undo link to its right.

Has anyone got a solution for my problem, please?

I suspect when the files were copied to the current system, some data did not make it.

First, let's see if your old profile is there.

https://support.mozilla.org/en-US/kb/how-run-firefox-when-profile-missing-inaccessible

http://kb.mozillazine.org/Profile_folder_-_Firefox#Navigating_to_the_profile_folder

https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles

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

Type about:profiles<enter> in the address box. How many profiles are listed? How many should be there? Also, open the profile folder in your file explorer.

https://support.mozilla.org/en-US/kb/recover-user-data-missing-after-firefox-update