Intermittent loading issues in Firefox

[humphd]

I tried going to http://learning.mozilla.org/codemoji and clicking the "Let's get going" link. My browser then hangs. I tried again and this time it made it to the onbording stuff at https://learning.mozilla.org/codemoji/#/onboarding/. I tried to repeat this with my cache clear, and the same thing happened again, this time with my console open. It is downloading 500+ SVG emojis, and maybe waiting on that to complete before going forward. At any rate, the end state doesn't always seem to happen for me, but since it's a first-time run issue in Firefox, I wanted to make you aware of it.

In Chrome it seems to work all the time. I know that Facebook deals with this by downloading a single image with all glyphs as one image and slices out the individual glyphs using CSS.