steps to reproduce: 1. Load marketplace-stage on Firefox Mobile Nightly (28.0a1) 2. Start the purchase of a paid app 3. Once the Webpay screen loads in a different tab, cancel purchase observed behavior: [JavaScript Error: "ReferenceError: push is not defined" {file: "https://marketplace-cdn.allizom.org/media/fireplace/js/include.js?b=4fec2ae-528d15a7" line: 6}] ID: fc504

I have noticed the same JS error while searching for :paid apps as well

Of all of the instances of the token "push" on line 6 of the minified source, the only ones that could throw that kind of ReferenceError are the ones that have to do with the tracking script (foo.push would throw a TypeError, only push() would throw a ReferenceError). That narrows it down. https://github.com/mozilla/fireplace/blob/master/hearth/media/js/tracking.js#L157 That looks like the culprit. Fortunately, it's not harmful since it happens inside an unload event. Low priority, but easy fix.