I had te same problem. The installed package version is 10, while firefox has version 9. To resolve this I had to remove ~/.mozilla/plugins/libflashplayer.so (don't know how it got there...) and reinstall flashplugin-nonfree.
I had te same problem. The installed package version is 10, while firefox has version 9. To resolve this I had to remove ~/.mozilla/ plugins/ libflashplayer. so (don't know how it got there...) and reinstall flashplugin- nonfree.