I tested it on Firefox, both an hour ago and now. No flickering at all, hovering, clicking, selecting, resizing the browser, Ctrl-+ing – nothing causes the flickering, not on the Firefox, that is.
EDIT: In Chrome :hover is not a problem, clicking causes hell of a flickering though :O (I just noticed that’s because you disabled the cubic-bezier transform)
> I have some JS controlling the icon but with JS disabled it still happens and JS is not touching the hover state.
Well, I tried disabling the JS anyways and… flickering stops :D