Hi mieczako:
This seems to be a recurring problem with CCleaner v7.x. If you search this CCleaner for Windows board for “Firefox bookmarks” you’ll find several topics from users who had their bookmarks, passwords and/or other Firefox Profile files (e.g., places.sqlite, favicons.sqlite, etc.) corrupted after upgrading to CCleaner v7.x.
See my 10-Mar-2026 post in devangelou’s Ccleaner deleted all my firefox bookmarks and backups for further details. There was some speculation in that topic that CCleaner v7.x will sometimes fail to prompt users to close Firefox before CCleaner begins the browser cleanup (or fails to shut down all Firefox background activity correctly if the user agrees to allow CCleaner to close Firefox), which in turn corrupts data in the user’s Firefox Profile during the cleanup.
I’m still using CCleaner Free v6.41 and never allow Health Check to run on my system [e.g., I changed Options | Settings | CCleaner Home Screen from Health Check (the default) to Custom Clean]. There might be a way to change the settings in Health Check to skip cleaning of your Firefox browser (see the support articles Using Health Check in CCleaner 7 and I’m using Health Check. Can I customize what is being cleaned?) but AFAIK you cannot permanently disable Firefox browser cleaning in the Health Check settings because Health Check always resets to its default settings after each clean. Unfortunately, most of the information about Health Check in the CCleaner Help Center is useless because many of those help articles haven’t been updated since CCleaner v7 was released in October 2025, so @Laurence_CCleaner will have to tell you if there is a way to permanently prevent CCleaner v7’s Health Check from cleaning your Firefox bookmarks.
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ASIDE:
If you use Custom Clean to clean your Firefox browser make sure that you have disabled the option to clean your Firefox bookmark backups. If your Firefox bookmarks are ever corrupted or go missing you want to be able to restore them from a recent backup (Bookmarks | Manage Bookmarks | Import and Backup | Restore) as described in the Mozilla support article Restore Bookmarks From Backup or Move Them to Another Computer. Firefox only keeps ~ 15 of the most recent bookmark backups and regularly purges older backups, and my Firefox bookmark backups use less than 15 MB of disk space. From my CCleaner Free v6.41:
As shown above, I’ve stopped using CCleaner to clean my Firefox browser, and I just use my Firefox settings (Privacy & Security | History | Custom History | Choose What You Want Firefox to Remember on Exit | Clear History When Firefox Closes | Settings) to automatically clear my cookies and temporary internet files each time I exit Firefox. See the section titled “How do I make Firefox clear my history automatically?” in the Mozilla support article Delete browsing, search and download history on Firefox.
As an extra precaution, I also manually backup my Firefox bookmarks (Bookmarks | Manage Bookmarks | Import and Backup | Backup) as a .json file and save them to a removable USB stick about once a week just in case the bookmark backups in my Firefox Profile are accidentally deleted or corrupted.
Dell Inspiron 15 5584 * 64-bit Win 10 Pro v22H2 build 19045.7725 * Firefox v156.0.0 * Microsoft Defender v4.18.26080.3-1.1.26080.3 * Malwarebytes Premium v5.7.0.328-164.0.5736 * Macrium Reflect Free v8.0.7783 * HDCleaner Portable 64-Bit v2.095 * CCleaner FreePortable 64-bit v6.41.11567