Start your Computer in safe mode with network support. Then start Firefox. Try Safe websites. Is the problem still there?

http://encyclopedia2.thefreedictionary.com/Linux+Safe+Mode Starting Any Computer In Safe Mode; Free Online Encyclopedia

Fred, thanks for the advice. I tried what you suggested with no results. I think I have not explained my problem clearly.

Let me try again. Whenever I open Firefox, I get a red strip near the top of the page (with white text) saying "The bookmarks and history system will not be functional because one of Firefox's files is in use by another application. Some security software can cause this problem."

In fact, I do not have any bookmarks and whenever I visit a website, it is not recorded in my History.

To the right of the message quoted above is a link to Mozilla support with suggested solutions to the situation. I have tried all of these with no success.

I found a solution, at least for my situation. In Windows 10, I installed a restore point that predated my problem. After this, I was able to restore my bookmarks from a backup in Firefox in accordance with the procedure shown here: https://support.mozilla.org/en-US/kb/restore-bookmarks-from-backup-or-move-them.

Please note, I was unable to restore the bookmarks using this method before I did the Windows restore point. Once I did the Windows restore point, I no longer got the error message about the bookmarks and history system, but I still did not have my old bookmarks until I restored them from the Firebox backup.

I hope this helps. Good luck.

That was very good work. Well done. Please flag your last post as Solved Problem so others will know.