User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.7; rv:19.0) Gecko/20100101 Firefox/19.0 Build ID: 20130215130331 Steps to reproduce: After upgrading to 20b1, the MutationObserver in my greasemonkey script no longer gets triggered. I use the script with the Scriptish addon. It works as expected after reverting to the prior beta version of Firefox. I have attached a simplified version of the script. I have another script that uses MutationObservers that still works, the only difference I can see offhand is that the attached script is using a document.querySelector as the target instead of just document as in the still-functional script. Actual results: The MutationObserver was not triggered. Expected results: The MutationObserver should have been triggered.

Please provide easy steps to reproduce : What do i have to do to trigger the issue ?

Dupe of bug 844406?

closed as dub -> no feedback from Reporter and error sounds same like written in comment 2 please feel free to open a new bug-report with more detailed information to reproduce if you can still see this problem in an actual firefox version