bug 682183 fixed!
Finally got the attachment reminder bug fixed! It was caused by the new web worker code in M-C. I spent about 5 hours reading up about web workers and how message passing is done between the creator of the worker and the worker. Both sides have to create a onmessage listener to listen for messages and use postMessage(data) to send messages.
Interestingly I was attending an OS lecture about threading the day before.
Anyway, the code in attachmentChecker.js was using legacy syntax to listen for messages. I simply had to change one line to fix it.
The fix came from ben turner. The guy that created the patch in M-C that caused tb regression. If only I had asked on IRC earlier. Well, it’s a lesson learned.