Thankfully, Flash has an equivalent of this effect--known as onion-skinning, an option that you can turn on that shows a range of frames both before and after your current frame, progressively fading them out as if they're layered on translucent paper on top of each other, or "onion-skinned". By dragging the edges of the greyed out block in your timeline you can expand or reduce the number of frames displayed in onion-skin mode, to let you better follow and track your animation.
The buttons for onion-skin mode can be found at the bottom of the timeline, to the far left before the division marking the layer control area. There are two buttons--one for onion skin, and to the right of that, one for onion skin outlines. Onion skin mode displays the solid images layered on top of each other (see the left-hand side of the image to the right of this page for an example), while onion skin outlines (on the right side of the image) only shows the outlines of the objects on each layer. Outline mode is recommended for long or detailed animations, as it's easier to render and scrub in realtime.