Comment 1 for bug 1507431

The Pipelight library, which is loaded by the browser, communicates through a pipe with the pluginloader.exe. The pluginloader.exe process will terminate itself as soon as the pipe is closed by the other side, so the number of process shouldn't grow unless the corresponding linux process is still alive. Firefox loads the plugins into a process called plugin-container, so you should take a look how many instances of plugin-container are still alive.