Look at the source code to "functions.php" and next to a number of lines is a little "arrow" that allows you to fold up comments, functions, and various other blocks of code. This is disabled in Instant IDE.
The Ace Editor is the Themer Pro code editor, but in Instant IDE Ace is an optional editor, but not the default. Monaco Editor is the default, which of course has different features. So just switch to the Ace Editor in the Settings pop-up in Instant IDE and see if that doesn't provide the features you're finding in Themer Pro.