Which Antivirus program and version are you using?

My antivirus also checks that. I'm using Avast, so under suspicions I checked "repair" and it then gives me 2 more options to which I answered "ask" and lastly "do nothing".

It is best to exclude the Firefox profile folder from scanning by security software to avoid files in the profile folder from getting corrupted or deleted.
Such warnings are usually false positives.

Did you just update the definitions in your unnamed antivirus recently?

I couldn't remember the full name, and it still pops up as malware and I remove it and it keeps coming back!

If it is detecting malware in the profile it may not actually be malware it may be a false positive.

In some instance if vital files are detected from the profile Firefox will attempt to recreate them, because they are needed for Firefox to work.

Some profile content will relate to Firefox addons, and because of the Firefox Profile's purpose the actual contents will vary between installations. The omni.ja file is one particular file prone to triggering alerts. The user.js file is one that is not present by default and is sometimes created by unwanted software.

Please let us know the name of the File, we can at least say what its purpose is. Malware may of course affect the profile.

Perhaps worth considering a full scan of your system using multiple and up-to-date tools on the presumption that you could have a malware issue.

 Sometimes a problem with Firefox may be a result of malware installed on your computer, that you may not be aware of.

You can try these free programs to scan for malware, which work with your existing antivirus software:

• Microsoft Safety Scanner
• MalwareBytes' Anti-Malware
• TDSSKiller - AntiRootkit Utility
• Hitman Pro
• ESET Online Scanner

Microsoft Security Essentials is a good permanent antivirus for Windows 7/Vista/XP if you don't already have one.

Further information can be found in the Troubleshoot Firefox issues caused by malware article.

Did this fix your problems? Please report back to us!

I use Avast, Malware Bytes and Hitman Pro, HITMANPRO is the only one that picks it up and deletes it!

As already advised It is probably worth adjusting regular scans and any automated cleanup not to run against the Firefox profile folders and files.

Next time it happens please let us know what it is that HitmanPro is deleting, and what message it is giving. I note HitmanPro is mentioned as using Behavioural Scan and maybe it is that generating a false positive.

Meanwhile as I said it may be worth considering using a full range of tools to scan the computer for malware.

Ran hitmanpro again and it deleted two suspicious items, used Snagit 8 to capture the screen area, it's attached..

If you set hitmanpro to find and delete certain cookies and it is able to do that without damaging anything then that is probably ok