To use Find and Replace in the way you're used to, select Find > Find and Replace in Files (Ctrl+Shift+F/Cmd+Shift+F). This brings up a modified version of the old Find and Replace dialog box. By default, this will search the entire current local site. Just change the "in" drop-down menu to Current Document, and work as before.
The drop-down menu is sticky, so it will remember your choice for future searches.