Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0
It used to be nice that I could open the same buffer in a second frame
(aka window). Sometimes I need to edit the same file in three or four
places and it's necessary to have all of them showing at the same
time... and for other reasons. But I tried doing "C-x 5 b" and also
"C-x 5 f" yesterday and couldn't do it either way. I could open a
different (not currently open file or buffer), but couldn't open the
same one. It worked years ago. Why take away perfectly good and useful
functionality? More importantly, how do I get it back?