I am not a professional in Ubuntu but able to successfully run my pipelight-plugin in my firefox.
Go to this website http://fds-team.de/pipelight/ and find out what is the problem with the browser.
If its user agent related problem then download a useragent switching addon like User Agent Switcher,User Agent Changer etc and switch it to windows platform.
Else if the problem is related to installation of silverlight in your ubuntu then
close the browser and update the plugin
sudo pipelight-plugin --update
and retest with http://fds-team.de/pipelight/
if problem persists then try to disable and reenable pipelight
sudo pipelight-plugin --disable silverlight
sudo pipelight-plugin --enable silverlight