I am on Ubuntu 18.04 using Wayland session. I installed many extensions trough Ubuntu Software > Add-ons > Shell Extensions to support my daily activities,
but I want to kill some of them because they sometimes slow down the computer, especially when I work with huge programs at the same time.
Is there a way to kill some specific extensions in Gnome Shell temporarily (just for the current session)?
Generally speaking, I'm not aware that any GNOME extensions seriously slow down the computer.
However...
Using standard Ubuntu tools, use Firefox (or other web browser) and go to https://extensions.gnome.org/local/. There you can enable or disable individual extensions at will.
To complete the task, restart GNOME Shell with ALT+F2, then r.
You can also use
GNOME Tweaks
(gnome-tweaks) to do the same thing (except for the GNOME Shell restart).