I updated my version of Firefox to 19.03 Beta only to have it be unable to download PDF. files. The file would download properly only it wouldn't be recognizable by Adobe Reader or FoxIt Reader as recognized file type. I tried five or six times with the same results, even to the point of disabling the plug ins. Finally I downloaded and installed version 18.02 and tried again, this time with success. For some reason the Beta version is not compatible with the Adobe or FoxIt plug-ins for PDF. Files.