You'd have to use a custom mapping or override the default FuzzyFinder mapping to start it. In there you can then check for an open NERDTree, and jump to the previous window (or maybe close NERDTree), like this:
:nnoremap <silent> <F5> :<C-u>if exists("t:NERDTreeBufName") && bufwinnr(t:NERDTreeBufName) == winnr() <Bar> wincmd p <Bar> endif <Bar> FufBuffer<CR>