In LayerManagerOGL::CopyToTarget(), we use glReadPixels to download the data from the GPU. glReadPixels implies glFinish, which means the preceeding glFinish here is redundant.
Everytime a useless glFinish call goes away, my personal happiness gets incremented.
Created attachment 578131 [details] [diff] [review] Remove unnecessary glFinish before glReadPixels in LayerManagerOGL
Derp, almost forgot the inbound: https://hg.mozilla.org/integration/mozilla-inbound/rev/e0dd8b223460