Hi DMF, That's a profile folder. Navigate to the folder, right click on it and Scan with MBAM again. Be sure Firefox is closed when you run the scan. The scan should tell you what MBAM sees as a PUP.

DMF said

I think the Question sums it up. After my Malwarebytes scan last evening it flagged the above captioned file as a PUP. Do I leave it in quaranteen? Delete it? Or mark it as OK? I am looking for some guidance here. Denny

What is the file and where is it claiming to be found ?

https://blog.malwarebytes.com/detections/pup-optional/

Also some malware and antivirus scanners claim things in the Cache is dangerous when they are harmless while in Cache if left alone to be deleted or overwriten by Firefox. Firefox cache file was infected with a virus

The disk cache would normally be in "AppData\Local".

It is possible that they found something in prefs.js or in one of the other files. Usually best is to exclude the Firefox profile folder in your security software as this usually causes issues with corrupted files or otherwise dataloss or malfunctioning.

You would have to contact Malwarebytes if you have questions about their software.