Sorry to hear about this problem.

First, if you haven't already, please do a normal shutdown and/or restart of your system. Restarting Windows can help by freeing up locked files, completing any deferred updates, and resolving temporary file permission issues.

Next, if Firefox still has bookmark problems, could you let us know what you get when you run the "Verify Integrity" diagnosis and repair function. That's here:

Open Firefox's Troubleshooting Information page using any of these methods:

• "3-bar" menu button > Help > More Troubleshooting Information
• (menu bar) Help > More Troubleshooting Information
• type or paste about:support in the address bar and press Enter

Near the bottom, there is a section titled Places Database -- that's the file which stores history and bookmarks. Click the button labeled Verify Integrity. There may be a 10-15 second delay before results appear.

If all is well, the report that appears below the button should start with:

> Task: checkIntegrity
+ The places.sqlite database is sane
+ The favicons.sqlite database is sane
> Task: invalidateCaches
+ The caches have been invalidated
> Task: checkCoherence
+ The database is coherent

Does yours say that, or something else? You can select and copy the report, and then paste it into a reply for review and comment.

Thanks for your reply in a different thread:

Here is a copy of report you requested. It is different from what you sent me. > Task: invalidateCaches - Unable to invalidate caches > 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.

Was there anything above those lines? Or was that the beginning of where your report was different from my example?

I keep getting the message “ and Bookmarks and history systems will not be functional because one of Firefox’s file is in use by another application.

It's possible that the file got locked for mysterious reasons if there's not currently an actual application locking it. Could you try the steps in this article: Fix "The bookmarks and history system will not be functional" error message.

I've already tried the Fix. I'm done.

We sometimes suggest to test Firefox in Windows' "Safe Mode with Networking". That's a mode where Windows skips over a bunch of stuff that usually starts automatically. If Firefox can access its bookmarks and history in "Safe Mode with Networking," that strongly suggests some outside program is causing the problem, even when you have deleted the file(s) and Firefox creates the new one(s).

If you want to try the test: https://support.microsoft.com/en-us/windows/start-your-pc-in-safe-mode-in-windows-10-92c27cff-db89-8644-1ce4-b3e5e56fe234