It sounds a bit similar to when a firewall program is blocking Firefox. Does anything in this article help: Configure firewalls so that Firefox can access the Internet?

Thanks for taking time to respond. I followed the instructions and removed Firefox.exe from the allowed list in the Internet security settings, and added it back. Unfortunately after restarting firefox, it did not launch the plugin container.

I should have added: look for plugin-container.exe as the program seeking to access the internet.

No luck, I added plugin-container as well as plugin-hang-ui. Restarted firefox and still no plugin container.

You would only see the plugin-container process if you have a web page with the Shockwave Flash plugin open in a tab.

• http://kb.mozillazine.org/Plugin-container_and_out-of-process_plugins

• http://www.adobe.com/software/flash/about/
• http://helpx.adobe.com/flash-player.html

Boot the computer in Windows Safe mode with network support (press F8 on the boot screen) as a test to see if that helps.

• http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/

I restarted the computer without launching in safe mode, tried to watch a video then firefox started to give flash player error. I reinstalled flash player and voila ! plugin container is active again. It probably prompted the error message to close before I could read and restarting the computer fixed it.

Thanks to both of you for taking the time to help. Have a nice day :)