Hi, not a expert here so try these :

• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data
• https://support.mozilla.org/en-US/kb/recover-lost-or-missing-bookmarks
• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox
• https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

• bookmarks and history: places.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)

RESTORE SESSION FILES (maybe)

• https://www.jeffersonscher.com/res/scrounger_json.html
• If a jsonlz4 backup can't be imported restored because it has the same structural problem as the database,
• a user can try to fix it using the Check/Repair JSON button on this page:
• https://www.jeffersonscher.com/res/bookbackreader.html

Out put HTML

Always :

• https://support.mozilla.org/en-US/kb/export-firefox-bookmarks-to-backup-or-transfer
• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

Weren't you able to reuse the old profile folder?

Do you only have one partition for root permission files and isn't there a separate partition for the Home directory?

If your home directory is on a separate partition then Firefox should have found the .mozilla/firefox folder with the profile automatically when you reinstalled Firefox.

Did you backup the entire profile folder including the bookmarkbackups folder with the compressed .jsonlz4 backups?

• https://support.mozilla.org/en-US/kb/restore-bookmarks-from-backup-or-move-them

Hi cor-el, thanks for your feedback. I do not have a separate folder for the HOME directory. Just a little digression: do you suggest me to make it in order to keep my settings and personal data when it's time for the next system upgrade? Back to the point, what I did it was a brutal copy of the .mozilla folder to another partition and then I've been copying single files to the new profile folder, including places.sqlite and the files of the bookmarkbackups folder, but it did not work. In fact, according to your last link, what I should have done was importing bookmarks from the automatic backups included in that folder, that's what I have just done and works like a charm. Now, how to recover the starting pages? Before ending this comment and also to recap:

1. the solution proposed in the link (importing from automatic backups) worked perfectly
2. do you suggest me to create a separate partition for the home directory and use it properly when it's time for the next system upgrade?
3. I accidentally marked your solution as "not useful", sorry for any inconvenience.

Regards.

When you install or update a new Linux version then the root partition will be formatted. If you only have one partition then this means that for home directory is lost. A lot of Linux distribution offer to create a separate partition for the Home directory that is preserved when you update the OS. You will have to reinstall all software that was installed on the root partition (e.g. in /opt or /usr), but at least you do not lose personal data. The root partition doesn't have to be that big (about 20 GB is usually sufficient), but keep an eye on folders like /tmp. You can check the current disk usage and distract the size of the Home partition.