There is a ongoing problem with Adobe Flash on Linux. In some situations clicking on flash enabled buttons does not work at all.
I have found a workaround that seems to restore the functionality.
Rename the mpviewer.bin file to npviewer.bin.real
cd /usr/lib/nspluginwrapper/i386/linux
mv npviewer.bin npviewer.bin.real
Then create a executable batch script called npviewer.bin
sudo nano npviewer.bin
it will contain the following lines
#!/bin/sh
GDK_NATIVE_WINDOWS=true /usr/lib/nspluginwrapper/i386/linux/npviewer.bin.real $*
Make sure that you make the script executable
sudo chmod a+x npviewer.bin
Restart your Firefox and that should do it.
This is from https://bugs.launchpad.net/ubuntu/+source/flashplugin-nonfree/+bug/410407/comments/143