The gallery is difficult to browse because the user must resize the window again and again, every time a new image is viewed.
First, resize Skitch to full-screen so I can see all the images in the gallery.
Next, double-click to select an image.
Uh oh! The Skitch app has automatically resized the window to a very small size that fits the image.
Ok, let's go back to the gallery to find another image.
The Skitch app keeps the small window size. I have to manually resize the window again to see all the gallery images.
Do not resize the window automatically. It is surprising behavior and causes repetitive window resizing. Instead, resize the content to fit the window.