Also surely you could just have:

  function readGIF(filename) {
    if (calcMemSizeNeeded(filename) > memoryFree()) {
      displayGifPlaceholder();
    }  
  }

eg just display an animated GIF if there's enough ram, and if not, display some placeholder.

I guess one of the other issues there though is websites that 'stream' animated gifs that never end. Still, you could just disable those for now.