Because IJFR is a OS X "service" it does not install or delete the same as an "App". To uninstall, drag the IJFR.app file to the trash, Empty the trash, and then reboot. Empty the trash again, and install the new version. The installer will log you out. Log back in and you should be good to go.
Click here to download IJFR V1.8.1 for Yosemite