>Firefox on Linux needs manual installation of Flash player. Surprisingly it’s bit messy, so here are a few steps to accomplish this task:

– Get the rpm/deb package downloaded on your system(typically titled adobe-release-i386-1.0-1.noarch.rpm/ flash-plugin-

– Install with YUM/aptget like follows:
$yum install adobe-release-i386-1.0-1.noarch.rpm

– Open Firefox browser, and in the address bar type “about:config”.
If you see flash player entry in there, you are fine. Else, go to next step.

– Run $updatedb
It’ll update the database for “locate” command.

– Run $locate libflashplayer
Most probably it will tell you the directory, “/usr/lib/flash-plugin” directory. Here you will find libflashplayer.so.

– Copy “libflashplayer.so” to Firefox installation directory (e.g. “/usr/local/bin/firefox/plugins/”). Also copy it to “/usr/lib”. This will make this library available to all users.

– Again check your Firefox browser with “about:config”. You should see a couple of flash player entries there.

That’s all. Try running Youtube for verification:-)

Ref: http://www.linuxquestions.org/questions/linux-software-2/how-to-install-flashplayer-in-firefox-487406/