The System Details list shows you use Firefox 66. I don't know in what Firefox version this menu item got added to the File menu, but it is in the File menu in Firefox 68. In Firefox 66 it is probably still in the Import and Backup menu in the Bookmarks Manager (Library). That is the third button on the toolbar in the library (hover each button and check the tooltips).

These instructions are for Firefox. Other browsers should also be able to do this.

These instructions will combine the new bookmarks with the old.

Open the Bookmarks Manager; Press the Alt or F10 key to bring up the toolbar, and select Bookmarks. Hot key is <Control> (Mac=<Command>) <Shift> B.

Once the window is open, at the top of the page, press the button labeled Import and Backup. Select Export Bookmarks To HTML, and follow the prompts and save it to a HTML file. Copy the file to another computer/profile. Repeat the instructions above, BUT select Import Bookmarks From HTML.

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

https://support.mozilla.org/en-US/kb/recover-lost-or-missing-bookmarks

Mozilla search: Import {web link}