Hey
I published a new version of the chrome extension yesterday. Chrome will be removing access to manifest version 2 at the end of this year, and the way objects are return is a little different.
For me it looks like I could most likely fixit it so you can again return arrays and objects, but for now, you need to make a little work around and return the object as json and then you could use JObject.parse or JArray.parse to convert it to something you could easily work with
( see an example here Detalle executeScript - #4 by Allan_Zimmermann )
I am very sorry for the inconvenience this gives.