Chrome has started installing pepperflash in the users' home directories instead of where freshwrapper is used to looking for it.
You can fix it by editing ~/.config/freshwrapper.conf to point to the .so file installed by chrome.
If you haven't already, you will need to [apt-get] install chrome [google-chrome-stable] for this to work, as well as browser-plugin-freshplayer-pepperflash . The pepperflashplugin-nonfree package, which in theory would work instead of installing chrome, appears to be broken.
Once you've installed freshplayer, you can find a template of freshwrapper.conf in /usr/share/doc/browser-plugin-freshplayer-pepperflash/freshwrapper.conf.example most likely.
I copied that file to ~/.config/freshwrapper.conf and then changed just one line to this:
pepperflash_path = "/home/[myusername]/.config/google-chrome/PepperFlash/22.214.171.124/libpepflashplayer.so"
You'll need to see exactly what path your libpepflashplayer.so is and use that.
This is a short term solution since presumably updates to chrome could move this (i.e., if 126.96.36.199 is a build number, this is likely to change often). Hopefully freshwrapper will be updated to look in ~/.config/google-chrome/... soon and this fix will become unnecessary (at which point you'll need to delete freshwrapper.conf again to enable the proper behavior...)
This is what worked for me, but I've only done a minimal amount of research on it to get it working, so there may be a more correct solution which I'm unaware of...