Assuming you're talking about :view, which is by default mapped to w key, you might want to change this mapping in vifmrc:
nnoremap w :view<cr>
to this:
nnoremap w :view<cr>gs
which will restore selection after command is executed.
It's not the viewer which resets the selection, but rather execution of most command-line commands behave this way. Introduction of a prefix command that disables resetting of selection was once discussed, maybe it's worth adding such a command.
UPDATE. Added :keepsel command (commit).