Nov 2017: Works okay as usual. I quit Firefox around version 30 or something and am back now with the Quantum version. The newer version of Norton ID Safe now logs me out several times over many hours when on Chrome or old Firefox it would keep me logged in all day as long as I did not restart my PC. Getting logged out at random isn't very helpful.

Jul 2021: For the past years the app has remained more reliable on Firefox. More recently I've noticed no issues and its helped quite a bit.