The script is here.
I don’t even know how to download it in a sensible format.
It’s a way for the Myfitnesspal app to be more useful for carb counting. I want to use it for diabetes management; ketoacidosis is not high on my list of things to do, despite the name of the plug-in.
Go to the link, look on the right side, and click the Download ZIP button.
A folder will appear in your downloads - open it, and click on the “MyFitnessPalForKeto.safariextz” file, and it should load it into Safari.
I haven’t done it, so I don’t know if there is any more required than that.
This is what I got.
Are you trying to do this on an iPad?
That plug-in is for Safari on a Mac.