Firefox web extension that loads reddit images directly instead of redirecting to the HTML page containing the image. This works for i.redd.it, preview.redd.it and external-preview.redd.it urls. Additionally, requests to www.reddit.com/media?url=$IMAGE_URL (i.e., the before-mentioned HTML page) are automatically redirected to $IMAGE_URL (i.e., the direct image url).
Note: a redirect to the original (high-res) image URL (the i.redd.it URL) can be preferred over the preview URL by changing the extension setting.