Close with middle click Gnome Flashback

[Jake.Werecat]

Hi Guys,
I'm running Ubuntu 20.04 LTS on my X61s with GNOME Session Flashback installed, so it kinda resembles Gnome 2. I must say that I like this GUI, though I'd really love to be able to close programs with middle clicking on bottom taskbar.
Here's a picture to support what i'm talking about.
https://i.imgur.com/CqPUrPs.png
I came across this extension:
https://extensions.gnome.org/extension/ ... -overview/
however it seems that it cannot be used with GNOME Session Flashback.