I think the flash thing is unrelated to your specific problem.

I am seeing the same thing on uploading pictures here on NAT with Firefox browser. The flash application to upload multiple pictures on NAT crashes and I have to do the alternative method and do one at a time.

I think this is related to Firefox and other browser updates that are phasing out some of the older add on browser additions and moving toward the phase out of Flash completely over the next several years.  Flash has been deemed too big of a security risk.

Have not updated Firefox to latest version yet as I I have many legacy add on's that will not be supported.

Have downloaded Waterfox which is virtually the same browser but is supposed to run legacy add on's.