I installed the Ignition Extensions module from GitHub (link below) on an Ignition 8.3.4 Gateway.
The module installs correctly and shows as Active in the Gateway module list, with no faults or warnings.
GitHub link:
The problem is that the module does not seem to load inside the Designer.
When I open the Script Console and run:
print dir(system)
There is no system.extensions namespace.
So the module is clearly active on the Gateway, but nothing shows up in the Designer.