So I have this issue, it seems that the smart developers decided to not allow approved opera extensions to be added to the default sidebar and instead it adds a gray sidebar.
As a web developer I need all the space and width of the screen i can get, so please add this feature to the next install of opera.
Other than this small issue I have uninstalled Google Chrome and made the switch
You can suggest it in Suggestions Box. In fact, it's something that some people have been requesting.
The original sidebar allows - in fact, only supports - extensions. The new sidebar (the one that is actually the nav bar from Speed dial and includes the messenger-type apps) does not. There have been requests to combine the two, see if you can find a thread about it in the Suggestion box forum and add your support there.