First of all:
if you are looking for extensions on
KMext - most of them are still usable with newest KMs.
It isn't obvious to find if some extension is actual or not. But it's really easy though takes some time: you should not install neither save - but OPEN desired link by clicking it.
It should open in your archive manager (7z, zip, rar etc.). Look at the folder structure. The extension is usually fully usable unless it contains folders
chrome
components
kplugins
modules
or
defaults
First 4 mean that this is adapted FF extension and nowadays they are installed differently.
Look the Extensions subforum for more info.
This thread may contain links and instructions on the installation for some of FF-derived addons.
When you see only
defaults folder (from wrong ones) - just unpack extension and change
defaults\pref path to
browser\defaults\preferences.
Now extension should work.
About AdBlock. Use
this package by manual unpacking it to your 75.1.
(NB! The original browser\omni.ja file will be ovrwritten!)