Mac OSX 10.6.8
Chrome, current update.
I got logged into roll20 for the first time, and the only thing I could see for the map was a black rectangle. I resized the map to 10%. It eventually showed me the map, after several minutes (even though everything up to that point had happened quickly enough). When I went to resize the map to 100%, it was a black rectangle again for several minutes. Then the map appeared. The GM altered the fog of war and the whole map (not just part) disappeared again. It stayed a black rectangle until I gave up several more minutes later.
I logged into the same game on a PC laptop, in chrome, and the map came up fine, after only a brief pause. It resized and scrolled, and fogged-of-war fine on this computer.
Any thoughts?