Hi suej:
See the Firefox support article Fix “The bookmarks and history system will not be functional” error message. Closing Firefox and restarting your computer (which hopefully forces CCleaner BETA 7 to release the lock on your Firefox files) will often solve this error. If your bookmarks don’t reappear after your computer is restarted the instructions in that article might help you create new favicons.sqlite and places.sqlite files in your Firefox user profile and recover your bookmarks .
If that doesn’t work see the Firefox support article Recover Lost or Missing Bookmarks. As noted in that article, Firefox automatically creates a backup of your bookmarks every few days and saves up to 15 of these backups in your Firefox user profile.
If you go to Bookmarks | Manage Bookmarks | Import & Backup | Restore this should display a list of recent bookmark backups (see my image below). Select the most recent backup to start the restore.
If your list of bookmark backups is empty then that means CCleaner BETA 7 has, unfortunately, also wiped your bookmark backups. If that is the case post back and let us know, since there might be another way to recover at least some of your bookmarks from an older Firefox profile.
Also let us know if you use another browser like Chrome or MS Edge on a regular basis, since you also have the option of importing bookmarks from another browsers into Firefox.
Dell Inspiron 15 5584 * 64-bit Win 10 Pro v22H2 build 19045.6218 * Firefox v142.0.1 * Microsoft Defender v4.18.25070.5-1.1.25070.4 * Malwarebytes Premium v5.3.7.209-139.0.5357 * Macrium Reflect Free v8.0.7783 * CCleaner Free Portable v6.39.11548 * HDCleaner Portable 64-Bit v2.091