In Firefox 69.01, neither Acrobat Reader or Firefox's viewer are available as a pdf default choice.
The default is Twinui, which appears to be in Microsoft Edge and is clumsy at best. The alternatives offered are not useful and do not include Acrobat Reader. Is there a way to add Acrobat Reader?
Additional System Details
- Shockwave Flash 32.0 r0; OpenH264 Codec & Widevine Conten Decryption Module
- User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:69.0) Gecko/20100101 Firefox/69.0
Problem solved. It was a Windows 10 problem.