Why doesn't Opera shut down the running task when a window or tab is closed ?

This just bloats the memory !

Thanks

Firefox has the about:config page to see all the available aspects, where you can change the boolean value to enable or disable

In firefox you get a warning before closing multiple tabs.

I want the default to be NO thumbnails (i.e. just a list of the text) , so I don't have to change the view every time I open bookmarks.

Thanks