If you have sync, and there is a problem anywhere, Shut Down Sync Immediately On All Devices to prevent the problem from spreading. Once the problem is fixed, perform the same repair on all computers/profiles before using sync again.

[v57+] Places Maintenance is built into Firefox.

Type about:support<enter> in the address bar.

You will find Places Database near the bottom. Press the Verify Integrity button.

When done, copy and post the results here.

https://support.mozilla.org/en-US/kb/fix-bookmarks-and-history-will-not-be-functional

Thank you. Results of Verify integrity:

> Task: checkIntegrity - Unable to check favicons.sqlite integrity: Error: Error(s) encountered during statement execution: > Task: invalidateCaches - The task queue was cleared by an error in another task. > Task: checkCoherence - The task queue was cleared by an error in another task. > Task: expire - The task queue was cleared by an error in another task. > Task: originFrecencyStats - The task queue was cleared by an error in another task. > Task: vacuum - The task queue was cleared by an error in another task. > Task: stats - The task queue was cleared by an error in another task. > Task: _refreshUI - The task queue was cleared by an error in another task.

I had already fixed the bookmarks loss part, so it's only clearing browsing history I can't do. I did re-start computer, no help. The link you included doesn't seem to apply to my problem.

Yesterday, Dec. 15, Firefox automatically updated to 84. Problem persists.

The places.sqlite file contains your History and Bookmarks. And it looks like it is corrupted.

Type about:support<enter> in the address bar.

Under the page logo on the left side, you will see Application Basics. Under this find Profile Folder. To its right press the button Show Folder. This will open your file browser to the current Firefox profile. Now Close Firefox.

Locate the above file. Then rename or delete it. Restart Firefox. The browser should then create a new place.sqlite and recover your bookmarks from the backup files.

Note: Your history is not backed up and will be lost.

This didn't work well. The history was deleted, which was good, but subsequently, Clear Recent History and Clear History commands continue not to function, so the original problem of not being able to clear history wasn't solved.

I wondered if the problem could be related to the fact that Firefox initially updated itself on top of or into my version 79, which had my bookmarks. So I put that in the trash and downloaded a new version, 84 at this point. Its new profile had no bookmarks, and when I tried to make the old profile the default instead, it was not allowed. So I have now reverted, because at least I have bookmarks, though no Clear History function.

Furthermore, during all that, Spotlight lost functionality, and the fixes that I've found for this do nothing. I ran Disk Utility, which I surmised might be helpful, but it was unable to do its job of checking/fixing indexing etc., or to completely verify the disk. I don't know if this is related or coincidental, or if other things have developed problems. Unfortunately, all these functions are essential to my work.

Thank you for trying to help. This has become too messy and difficult for me, so I am likely going to revert to Firefox version 79. The more I see of Firefox 83 and 84, the less I like it.

Try running Places Maintenance again.

Make sure you do not run Firefox in permanent Private Browsing mode (Always use Private Browsing mode; Never Remember History).

• https://support.mozilla.org/en-US/kb/private-browsing-use-firefox-without-history
• https://support.mozilla.org/en-US/kb/common-myths-about-private-browsing

• Options/Preferences -> Privacy & Security
  Firefox will: "Use custom settings for history"
• remove checkmark: [ ] "Always use Private Browsing mode"