Mozilla was so eager to get WhatsApp on Firefox OS that it wrote a proof of concept J2ME.js interrupter [1] (repurposing Shumway's Flash-to-JS JIT) to run WhatsApp's Java applet. But WhatsApp was not interested. This was a big blow because lack of WhatsApp support was one of the top complaints or deal breakers for Firefox OS users in its initial markets.

[1] https://github.com/mozilla/pluotsorbet