A separate plugin-container.exe process is started for each plugin (e.g. the Adobe Flash plugin, Adobe Reader plugin, or the Java plugin), the first time you visit a webpage that needs that plugin. _{EDIT: On Windows, Java is the exception since, by default, it doesn't use plugin-container (bug 603417).} When you exit Firefox, all of the plugin-container processes for those plugins should be terminated (although in rare cases, the process may need to be terminated manually, in the Windows Task Manager). More info here:

• What is plugin-container _{EDIT: and http://kb.mozillazine.org/Plugin-container_and_out-of-process_plugins}

If you are having problems with memory or CPU usage because of a plugin-container.exe process, you could find out which plugin is involved by restarting Firefox so that no plugin-container.exe processes are running, then disable all plugins except for Adobe Flash - see Troubleshoot issues with plugins like Flash or Java to fix common Firefox problems for details. Then visit YouTube or another Flash-enabled site and check the plugin-container process in Windows Task Manager. When you finish testing, restart Firefox and try the same test with another plugin.

If the problem turns out to be the Adobe Flash plugin, start by disabling hardware acceleration in Flash settings. See these articles for more information:

• http://kb.mozillazine.org/Flash#Performance_or_display_issues_with_certain_Flash_videos
• Flash Plugin - Keep it up to date and troubleshoot problems under Troubleshooting

So that would be a no? That FireFox dont have a task manger style "app"

Maybe one of these utilities can help:

• http://technet.microsoft.com/en-us/sysinternals/bb896653.aspx Process Explorer
• http://technet.microsoft.com/en-us/sysinternals/bb896645.aspx Process Monitor

Correct, Firefox doesn't have its own task manager.

I wanted to correct something I said earlier. On Windows, the Java plugin no longer runs out-of-process in recent versions of Firefox so it doesn't involve the plugin-container process (ref.). In other words, when you see plugin-container.exe running, it's for other plugins, NOT Java.

See http://kb.mozillazine.org/Plugin-container_and_out-of-process_plugins#Windows_and_Linux for details.