Would be helpful if you gave us a summary of what "fixes listed on line" that you have already tried.

Which security programs and anti-malware programs do you have installed? Typically, those are the prime cause of Firefox files being in use by another application and causing that message appear when Firefox being launched.

Boot the computer in Windows Safe mode with network support to see if that has effect in case security software is causing problems.

• http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/
• http://www.7tutorials.com/4-ways-boot-safe-mode-windows-10

Hi thank you. I've tried renaming the places.SQLite file. I'm using the standard Microsoft antivirus on Windows 10. I'm not confident about using safe mode but have tried adjusting the anti virus settings

Try to use the process explorer utility to check what application has a handle on the places.sqlite file.

• https://docs.microsoft.com/en-us/sysinternals/downloads/process-explorer