How to expand the Formula field in Conditional formatting

I very often use Conditional formatting based on a formula and very often large (long) formulas.

My problem is that I find it very difficult to edit this long formulas, as I only can see a small part of the formula in the small formula box, and when I try to move the cursorposition with use of the arrow keys Excel inserts a new cell reference.

Is there a way to "expand" the formula field or any hints for easy editing of long formulas?