Firefox: TypeError: steal.dev is undefined

We have created a new Javascript MVC application and just put it out to beta. I've got this error repeated 35 times on a single day in the logs:
    error_message: TypeError: steal.dev is undefined
    error_file: http://beta.volunteerspot.com/jquery/model/model.js
    error_line: 1751
    client: Mozilla/5.0 (Windows NT 6.0; rv:21.0) Gecko/20100101 Firefox/21.0

It's only Firefox (one version 12, one version 16, and the rest version 21 - mixed Windows and Mac OS). It doesn't happen for me on any of the machines I have access to test on.

My line 1751 of model.js is (in the destroyed function):

1. steal.dev.log("Model.js - "+ constructor.shortName+" "+ funcName);