If you are having trouble viewing Youtube in Mozilla or Seamonkey on your Linux machine, this guide will help you.
Chances are your Linux distribution came packaged with a copy of Mozilla. The only thing you need to do after your linux installation is update it to a copy of the most recent version. This can be done using a package manager.
I personally like using SeaMonkey, because it comes bundled with IRC and some other stuff. If you want install the Sea Monkey Browser, you can download the 32 bit version and if you dig around you can also find the 64-bit version.
Now if you have a 64-bit version of Mozilla or SeaMonkey, you are interested in doing the following:
Download flash for your 64 bit Linux Operating System and save it to your Downloads folder. Extract it with tar xfv 'flash-package-name' to the same Downloads folder. You will find a file called libflashplayer.so. You want to copy this file to /usr/lib64/mozilla/plugins. Make sure you specify lib64 and not lib. This is the same as Program Files x86 and Program Files on Windows. Program Files x86 on Windows and lib on Linux corresponds to 32-bit. Program Files and lib64 corresponds to 64-bit.
After you cp libflashplayer.so /usr/lib64/mozilla/plugins, both Mozilla and SeaMonkey should work fine.
Now what if you downloaded a 32-bit version of SeaMonkey, (which is usually the default download)? Well you may run into a problem where SeaMonkey can't play a YouTube video. This is because there is no copy of libflashplayer.so in the 32-bit directory - /usr/lib/mozilla/plugins.
Save yourself some trouble and do NOT cp the 64-bit libflashplayer.so file to /usr/lib/mozilla/plugins. If you this, you will be able to play the video, but there will be no audio. To circumvent this issue, go back and download a 32-bit flash plugin from the flash website. Extract this file in another directory. Then copy this 32-bit libflashplayer.so file into the directory /usr/lib/mozilla/plugins.
And that should fix it.