Have a look at your developer console. There is an error which states that the image is truncated. It cannot be cached correctly by Firefox. Apparently other browsers can but with larger files would probably fail too.

Base64 is a string filled with groups of four 6-bit characters (A-Z, a-z, 0-9). An image in Base64 is always at least a third larger than a binary image file. Your users’ CPUs need to do extra work to decode the image.

Would your application be able to work with blobs instead? If so, then you would be able to use createObjectURL