I have tried all 3 versions of the editor on your website with Safari (latest version) and am having the same problem with the popup font colour and Highlight popup boxes. Here are a couple descriptions from my clients

Firefox
Version 2.0.0.12

Text 'jumped' when selecting, sort of 'jittery' but workable.

Safari
Version
3.0.4 (523.12.2)

initial opening of colour palet the main window was all black but the small window on the top right showed the colour.  When I changed the quality to med the main pallet worked and then when I changed back to high quality it was ok.. so a little buggy.  Ok alot buggy.. clicking the mouse does not lock the colour so when you move the mouse to click ok the colour changes..

the text did not 'jump' when I selected by dragging the mouse.

Can you help?

thanks