Performance has improved considerably. However, there is still a major outstanding bug, due to the rendering of window transparency[1].
Window transparency can be turned off by setting "gfx.compositor.glcontext.opaque" to true in about:config. This will cause a minor degradation in appearance of the window frame and tabs, but it will improve performance and extend battery life.
I have had it set for over 6 months and am anticipating the resolution of this outstanding bug.