Ok, it probably tries to do something not allowed in the background context.

Is there a way to close the issue? - It's not a bug, it's just a 'would be nice to have' if it is technically possible, but it is an 'experiment' so I guess nobody's gonna waste time with it...

btw. I edited the original comment later, adding #enable-fast-unload - it was just something I thought about, but didn't expect to be the cause at all. So, now at least anyone with the same issue knows they cannot use both at the same time.

Same. Renders extension unuseable.

Clicking 'green X' in Tabs Outliner window does the same. 'Tab-rows' remain in weird state. Clicking or closing it afterwards does nothing. Only manual 'trash' closes it. Closed windows become gray instead of being closed, with all their tabs still blue in them.

First observed after updating to 59. I use #enable-fast-unload if it could matter... (other extensions react to closing tabs fine, though)

OS: Ubuntu x86_64 GNU/Linux 4.4.0-83-generic

Chrome: 59.0.3071.115 (Official Build) (64-bit)

Tabs Outliner: 1.4.130