I've been trying to download the Flash Player installer using Firefox 47 in Ubuntu 15.10. When I click Download Now the URL in the address bar changes to "apt:adobe-flashplugin?channel=$distro-partner" and as it's not an address that Firefox understands it tells me:
The address wasn't understood
Firefox doesn't know how to open this address, because one of the following protocols (apt) isn't associated with any program or is not allowed in this context.
You might need to install other software to open this address.
This happens with both paths to download Flash Player, download for this machine and download for another machine.