by 
I have CentOS 6.5 installed on my laptop for quite sometimes but I am rarely using it. Recently, I started using it again because I was little bit bored with Ubuntu and surprisingly found that none of browsers could play Flash video. Previously, on the time configuring the system I have installed Adobe Flash video from Adobe official website which made browsers to play Flash videos. When I have tried to install the plugin again, it gave me the message that the plugin is already installed. After little bit of search I have found the solution here.
For 32-bit x86 install the following packages,
$ rpm -ivh http://linuxdownload.adobe.com/adobe-release/adobe-release-i386-1.0-1.noarch.rpm
$ rpm --import /etc/pki/rpm-gpg/RPM-GPG-KEY-adobe-linux
And for 64-bit x86_64,
$ rpm -ivh http://linuxdownload.adobe.com/adobe-release/adobe-release-x86_64-1.0-1.noarch.rpm
$ rpm --import /etc/pki/rpm-gpg/RPM-GPG-KEY-adobe-linux
$ yum check-update
$ yum install flash-plugin nspluginwrapper alsa-plugins-pulseaudio libcurl
After that just restart your browser and everything should be fine.
