All links to external sites open new windows, but within themes, e.g. if you leave a new window open after opening a music link, the next music link will open in that window, but a Bat link will open a new window (reused by the next Bat link).
External links may have popups - I donšt see any since I use Firefox with popups blocked by default.

Within the frames, back goes back to wherever you were (javascript)