Note that, according to the Mozilla support document Use the Adobe Reader plugin to view or download PDF files | Firefox Help "Beginning with Firefox version 52, support has ended for all NPAPI plugins except for Adobe Flash.
To download previous version of ACROBAT READER, go to Adobe Acrobat Reader DC Install for all versions To download the latest version of ACROBAT READER, go to Adobe Acrobat Reader DC Install for all versions. Thus far we've only been discussing Flash Player, even when I posted instructions to install Flash Player you NEVER mentioned ACROBAT READER, until now. You are posting to the FLASH PLAYER forums - two completely different products. The plugin you are referring to, as clearly identified in your screenshot, is ACROBAT READER.
Follow on-screen instructions to install Flash Player.Click on the DMG file to mount the installer.
Locate Flash Player installer saved on your system.Flash Player installer will be downloaded and saved to your default 'save to' location.In step 2 select which browser you wish to install Flash Player for.To install Flash Player on OS X 10.8, do the following: With that said, while OS X 10.8.5 is no longer supported Flash installation is not blocked. Apple themselves no longer support OS X 10.8, as the last update for 10.8 was in 2015 ( Apple security updates - Apple Support ). It is not any company's responsibility to continue supporting old operating systems, and companies routinely stop supporting older operating systems.