Hi, welcome!
Fijjiontrack is an ImageJ plugin for fission-track analysis.
You can find our jar file Fission_Track_Counter-(version).jar on the main page.
We keep the latest two versions and you can just choose the most up to date one.
You can drag and drop it to Fiji and find our plugin from Plugins->Fission Track Counter->Fission Track Counter
You can also customize your own path when you drag and drop our plugin.