I've experienced the same problem. However I think I can provide a hint. When install is requested via sudo apt-get install flashplayer-nonfree, the process halts after a "Downloading" message.
As a workaround, you can install the Flash player directly within firefox visiting any page with Flash content and clicking on the puzzle icon that is shown in place of the missing flash content. -- Flash stalls on install freezing synaptic https://launchpad.net/bugs/58808 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
