So Superfast, what you're saying is get rid of old MozBackup files and keep the most recent?
Safest way (to be sure) is to Start/Run/%Appdata%/Enter & copy Mozilla folder to the desktop or some other easy to find folder so that if anything bad happens, you can always restore it.
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1) Then, download & run MozBackup. Go through the options & keep what items you want. Save the backup to the desktop or where-ever you can easily find it. It will be a single file.
2) Delete the %appdata%\Mozilla folder & let Firefox create a brand new profile.
3) Close Firefox, & use MozBackup, but THIS time, use the restore function & navigate to your saved settings to open them. It will prompt you that it may overwrite files already present in the profile. Let it, & when it has finished, open Firefox & your browser will now have the new profile container with the old Firefox settings.