honestbleeps/Reddit-Enhancement-Suite — pull request #1077 by matheod (2014-05-15 18:52:54+00:00)
Title: Avoid a strange bug making the appendChild didn't work under strange con...

...ditions

It's ugly, but I think it's a king of bug from Google Chrome

Disable, then enable the extension, reload the page, open the alert => no overlay
A way to make it work is to open the console, reload the page then open the alert.
After that alert will always work (until disable/enable the extension).