[mozillalives]

Here's my two cents.

1. Make sure you've told your boss that you are not being challenged and that you really want to work on something that will challenge you. Perhaps you have already done this, but I still mention it because sometimes we can have a difficult time being direct and saying exactly what we mean. Make sure that they know you are grateful for the position but from what you were told during the hiring process, you were going to have more challenges. This may help you get the challenges you were looking for, but even if it doesn't it will help you when you need to explain why you have to leave. (If you have to leave, exit gracefully. I cannot emphasize this enough.)

2. Make sure you're open to challenges. Are there other challenges around you that you can work on? Sometimes the best challenges are not the ones you go looking for. Sometimes the best lessons come from unexpected challenges.

3. Keep open to new places and don't hide what you're doing. Explain clearly why you would be leaving - you were told that it would be challenging but once hired that changed. Honesty is your best policy here because hiding anything will be a red flag to anyone who scrutinizes your experience.

Not very original, but I hope it helps.