Nexus 4 running recent nightly. Go to https://bugzilla.mozilla.org/show_bug.cgi?id=1047127 and click on the link to the profile aaron posted. This starts a download. Open the notification tray and tap on the download entry. This pops up a dialog to cancel the download. The buttons say "undefinedNo" and "undefinedYes" instead of "no" and "yes".
Created attachment 8471051 [details] [diff] [review]
This is actually a regression from a fix to the JS engine in bug 369778. RegExps now return undefined instead of "" for unmatched conditions. This is the same fix used in CommonDialog.js for Desktop.
I also saw a similar issue in the slow script dialog checkbox last night. Will this fix that issue as well?