When uploading large images the upload window get's stuck. What is the file limit for a image file? Why don't I get an error then upload fails (XHR itself is not returning anything)?
The maximum non-animated file size you can upload is 10MB. However, if the image is over 1MB then it will automatically be compressed or resized to 1MB, for better viewing on the net. The maximum animated file size (both GIF and PNG) is 2MB.
It might be a network error on your side.