Turn off Hardware acceleration on your browser or keep the idle clocks at 300. More than likely your browser needs more core speed on the gpu or voltage or it artifacts.
I haven't had any bottom screen flicker since I've changed the Idle clocks to 300/300, but I still get an occasional full screen flicker or middle line in the center of my screen. Doesn't matter if a browser is open or not.
And I haven't had hardware acceleration enabled on the browser since that feature was released.