Moonlight is an open source implementation of Microsoft Silverlight for Unix systems. With Moonlight you can access videos, applications and content created for Silverlight on Linux.
(Source: go-mono.com)
To install Moonlight plugin, go to http://www.go-mono.com/moonlight/
If you can't access above page, try this: http://mokeke.sytes.net/downloads/linux/Novell_Moonlight/
Firefox
In Ubuntu 12.04 64-bit, Moonlinght plugin for Firefox v12 worked easily just by installing the plugin.
After updated to Firefox v13, Moonlight plugin disabled. I removed and reinstalled the plugin and it start working again.
Chromium
By the date 2015, Chromium (and also Google Chrome) will no more supporting NPAPI plugins. That means Moonlight plugin no more works.
In Ubuntu 64-bit, Chromium Moonlight plugin doesn't worked for me. While after I tried something and worked! Here are the steps I followed.
Step 1. I downloaded 64-bit Moonlight plugin for Chromium from www.go-mono.com.
(Note that 64-bit is for me. You may need another)
Step 2. I renamed the downloaded file extension from .crx to .zip and extract the content to Chromium plugin folder which it is /usr/lib/chromium-browser/plugins
If you're using terminal, no need to change the extension. unzip can extract the content of the .crx file directly.
$ sudo unzip novell-moonlight-3.99.0.3-x86_64.crx -d /usr/lib/chromium-browser/plugins
Step 3. I started Chromium and Moonlight plugin worked for me.
Test If Moonlight / Silverlight Is Installed
Sometimes I am looking for a sample to test if installing success and Silverlight application works.
If you are also in same situation, you can try the silverlight audio player (developed by me) that currently used in the following pages.
Update: 2014/05/22
I realized that Moonlight giving errors when trying to download "Microsoft Media Pack".
I get silverlight-media-pack-linux-x64-21-1.so from another computer and put it in ~/.mozilla/plugins/moonlight/ folder.
Then Google Chrome and Firefox succeed to play audio/video using Moonlight. But it's a pitty that I couldn't succeed with Chromium.