What task manager are you talking about? I ran “sudo killall firefox”.
I run “No Script” plugin for Firefox.
And the “task manager” is called “Task Manager” under this Debian Distribution.
This machine is running Debian 8.1.0 install with XFCE GUI. I previously ran XUbuntu, which also runs XFCE GUI. My first linux distribution which ran XFCE was Redhat 8.0, it was not part of the install, but I added it.
I hate bloat on any computer install.
My first Linux OS was installed dual boot under MSDOS (in 1994). It was a flavor of Slackware, without a GUI. It was very small and fast. Really liked that OS.