I would like to point out that I am having trouble as well. It seems there was a recent update to the firefox plugin, and when I connected to the remote machine (both using Win7 64-bit), I cannot use my keyboard. The mouse is inside of the remote screen, so it should capture the keyboard useage, but it does not recognize it.
I also tried on IE9 (64-bit), and the same issue occured. Any suggestions would be helpful.