@xaizek thank you - both are working well
the first one
nnoremap <silent> <PageDown> <C-w>w5j<C-w>w
nnoremap <silent> <PageUp> <C-w>w5k<C-w>w
is scrolling down and up

what is RHS?
RHS means right-hand side: the command or key sequence Vifm executes instead
LHS means left-hand side: the key sequence you press
example:
nnoremap <F5> :mkdir< space>
LHS: <F5>
RHS: :mkdir<space>
the second one
set previewoptions+=toptreestats
gives number of dirs and files on the top

However, as you may notice, for large trees it can take a few seconds.
Is it possible to make a mapping like this, to go in :view mode and go at the bottom of the tree:
nnoremap w :view <cr><c-w>wG