Tested in Opera.
Shift + Enter does not work to popup a wiki search in a new browser page or tab on WMF sites. I think it's because of the Vector extension's changes the search box. I've lost a lot of work on Wikipedia when I try to find a cite or other info, and then the Vector search box causes my browser to leave my work unsaved, and lost forever.
This seems to be related, but describes slightly different phenomena for a different extension: