You need to install flash, multimedia codecs and some other things. When you
install Windows you must add to it too. You add drivers, codecs and
applications. Ubuntu gives you a working system, but you need to tweak and
add some things to get it working. Ubuntu does not come with them
pre-installed, so you must add them. They are packaged together to help.

First thing to ask is did you install the ubuntu-restricted-extras? You can
do this from Software Centre or from the commandline. Just search for
restricted-extras and it should show. Install it. Or you could open a
terminal and cut and paste this: sudo apt-get install
ubuntu-restricted-extras

After it is installed try your sites again. If they don't work, post another
request fro help with links to the sites and what is happening or not
happening when you go there.