There should be a checkbox in the special characters box in the advanced visual rich text editor to hold the box steady there. If I for example want to write in Greek, it's a pain in the backside to open the box, select the character and then open the box again, because it disappears.
So when the checkbox is on, the special characters box wouldn't disappear, so one could just click on the special characters buttons and yay, writing made easy! Then, just before putting on the last character, uncheck the checkbox, and the last character will appear on the screen and the box would disappear normally.
I believe it would be useful. Also, if there's some Shift, Ctrl whatever some key combination, hotkey or easter egg to already do this function, I don't want to hear it. It just proves that it isn't too easy to find and thus, use.