@Jonathan
For some reason even your CodePen example with rotation: 0.01 gives me a non-smooth animation on Firefox.
Moreover, if I switch browser tabs or hide/show your inline CodePen example by clicking the "Results" button, it gets even worse.
Probably the rendering algorithms in Firefox have been updated since 2015.
I understand this is a Firefox issue unrelated to GSAP, however, maybe there are some tips on fixing this behavior.
Thank you!